Evaluation of enzyme immunoassay (EIA) as a screening method for hepatitis B markers in an open population.

Commercially available kits for detection of hepatitis B surface antigen (HBsAg) and hepatitis B surface antibody (anti-HBs) by enzyme immunoassay (EIA) were evaluated in American Samoa during a public health programme to eliminate the transmission of hepatitis B. The first 19,184 serum specimens obtained, representing 68% of the total cooperating population, were initially tested for anti-HBs, and those without detectable antibody were tested for HBsAg. All the antigen-positive serum samples, and a selection of the antigen- and antibody-negative specimens were tested by radioimmunoassay (RIA) for detection of both markers.

Protein import into the yeast mitochondrial matrix. A new translocation intermediate between the two mitochondrial membranes.

Import of authentic or artificial precursor proteins into the matrix of isolated yeast mitochondria can proceed via a translocation intermediate that is lodged between the two mitochondrial membranes. The intermediate accumulates when import is arrested by depleting mitochondria of ATP. Generation of the intermediate requires a potential across the inner membrane.

Sequential action of mitochondrial chaperones in protein import into the matrix.

Translocation and folding of proteins imported into mitochondria are mediated by two matrix-localized chaperones, mhsp70 and hsp60. In order to investigate whether these chaperones act sequentially or in parallel, we studied their interaction with newly imported precursor proteins in isolated yeast mitochondria by coimmunoprecipitation. All precursors bound transiently to mhsp70.

Protein import into mitochondria: two systems acting in tandem?

Mitochondria can import proteins from the cytoplasm at sites where the two mitochondrial membranes are closely apposed. However, each of these membranes contains a distinct protein translocation channel. Recent evidence suggests that the two types of channel are not permanently coupled, but may dissociate in a reversible manner.

Availability and use of hepatitis B vaccine in laboratory and nursing schools in the United States.

Hepatitis B is a well-documented occupational hazard for health care workers, including both laboratory and nursing personnel. Since the development of effective hepatitis B vaccines, the Immunization Practices Advisory Committee (ACIP) has recommended that health care workers receive the vaccine. In this study, 78 laboratory training programs and 83 nursing training programs were surveyed regarding availability and usage of hepatitis B vaccine.

The MAS-encoded processing protease of yeast mitochondria. Interaction of the purified enzyme with signal peptides and a purified precursor protein.

The matrix of yeast mitochondria contains a chelator-sensitive protease that removes matrix-targeting signals from most precursor proteins transported into this compartment. The enzyme consists of two nonidentical subunits that are encoded by the nuclear genes MAS1 and MAS2. With the aid of these cloned genes, we have now overexpressed the active holoenzyme in yeast, purified it in milligram amounts, and studied its biochemical and physical properties.

Inner membrane protease I, an enzyme mediating intramitochondrial protein sorting in yeast.

Several precursors transported from the cytoplasm to the intermembrane space of yeast mitochondria are first cleaved by the MAS-encoded protease in the matrix space and then by additional proteases that have not been characterized. We have now developed a specific assay for one of these other proteases. The enzyme is an integral protein of the inner membrane; it requires divalent cations and acidic phospholipid for activity, and is defective in yeast mutant pet ts2858 which accumulates an incompletely processed cytochrome b2 precursor.

Mitochondrial proteins essential for viability mediate protein import into yeast mitochondria.

Only five mitochondrial proteins are known to be essential for viability of the yeast Saccharomyces cerevisiae; all of them are key components of the mitochondrial protein import system. Other components of this system are not essential for life; they include functionally redundant import receptors on the mitochondrial surface and enzymes acting upon only a few precursor proteins.

A yeast mitochondrial outer membrane protein essential for protein import and cell viability.

The gene encoding ISP42, an integral outermembrane protein located at the yeast mitochondrial protein import site was cloned, sequenced and modified. Yeast cells depleted of ISP42 accumulate uncleaved mitochondrial precursor proteins and then die. ISP42 is the first mitochondrial membrane protein shown to be indispensable for protein import and cell viability.

A precursor protein partly translocated into yeast mitochondria is bound to a 70 kd mitochondrial stress protein.

We have probed the environment of a precursor protein stuck in mitochondrial import sites using cleavable bifunctional crosslinking reagents. The stuck precursor was crosslinked to a 70 kd protein which, by immunological techniques, was shown to be a matrix protein. The protein was purified to homogeneity by ATP-Sepharose chromatography and partially sequenced.

The MAS-encoded processing protease of yeast mitochondria. Overproduction and characterization of its two nonidentical subunits.

The amino-terminal presequences of proteins imported from the cytoplasm across the mitochondrial inner membrane are cleaved off by a soluble matrix-localized protease composed of two nonidentical homologous subunits. In the yeast Saccharomyces cerevisiae, these are encoded by the nuclear MAS1 and MAS2 genes. We have now constructed yeast strains in which either one or both of the genomic MAS genes are controlled by a galactose-inducible strong promoter.

Protein import into yeast mitochondria is accelerated by the outer membrane protein MAS70.

The yeast mitochondrial outer membrane contains a major 70 kd protein with an amino-terminal hydrophobic membrane anchor and a hydrophilic 60 kd domain exposed to the cytosol. We now show that this protein (which we term MAS70) accelerates the mitochondrial import of many (but not all) precursor proteins. Anti-MAS70 IgGs or removal of MAS70 from the mitochondria by either mild trypsin treatment or by disrupting the nuclear MAS70 gene inhibits import of the F1-ATPase beta-subunit, the ADP/ATP translocator, and of several other precursors into isolated mitochondria by up to 75%, but has little effect on the import of porin.

Properties of avian retrovirus particles defective in viral protease.

The structural and enzymatic components of retroviral cores are formed by proteolytic cleavage of precursor polypeptides, mediated by the viral protease (PR). We constructed an active-site mutation, D37I, in the PR of avian leukosis virus. The D37I mutation was introduced into an infectious DNA clone, and quail cell lines expressing the mutant virus were established.

Development of recommendations for control of hepatitis B virus infections: the role of cost analysis.

Hepatitis B (HBV) infection produces a number of acute and chronic consequences including fulminant hepatitis, chronic liver disease and cirrhosis. The development of safe and effective hepatitis B vaccines has led to the development of several prevention strategies based on the endemicity and primary age of infection in the population. In areas of high endemicity of infection, universal immunization of infants has been advocated and appears feasible.

The mitochondrial targeting function of randomly generated peptide sequences correlates with predicted helical amphiphilicity.

A pool of oligonucleotides encoding a start methionine and nine random amino acids was inserted at the 5'-end of the gene for the yeast cytochrome oxidase subunit IV lacking its own mitochondrial targeting sequence. Approximately one-quarter of the randomly generated sequences targeted subunit IV to its correct intramitochondrial location in vivo. Sequence analysis of 89 randomly generated sequences showed that their efficiencies as mitochondrial targeting signals correlated with the potential to fold into an amphiphilic alpha-helix.

Protein import into mitochondria: ATP-dependent protein translocation activity in a submitochondrial fraction enriched in membrane contact sites and specific proteins.

To identify the membrane regions through which yeast mitochondria import proteins from the cytoplasm, we have tagged these regions with two different partly translocated precursor proteins. One of these was bound to the mitochondrial surface of ATP-depleted mitochondria and could subsequently be chased into mitochondria upon addition of ATP. The other intermediate was irreversibly stuck across both mitochondrial membranes at protein import sites.

Translocation of proteins across the mitochondrial inner membrane, but not into the outer membrane, requires nucleoside triphosphates in the matrix.

Work in several laboratories has established that import of proteins across the mitochondrial inner membrane requires an electrochemical potential across that membrane and cleavage of nucleoside triphosphate. We now show that nucleoside triphosphate must be present inside the inner membrane. In contrast, the potential-independent insertion of porin into the outer membrane requires ATP only outside the inner membrane.