The structure of Aquifex aeolicus ribosomal protein S8 reveals a unique subdomain that contributes to an extremely tight association with 16S rRNA.

The assembly of ribonucleoprotein complexes occurs under a broad range of conditions, but the principles that promote assembly and allow function at high temperature are poorly understood. The ribosomal protein S8 from Aquifex aeolicus (AS8) is unique in that there is a 41-residue insertion in the consensus S8 sequence. In addition, AS8 exhibits an unusually high affinity for the 16S ribosomal RNA, characterized by a picomolar dissociation constant that is approximately 26,000-fold tighter than the equivalent interaction from Escherichia coli.

DDX1 is an RNA-dependent ATPase involved in HIV-1 Rev function and virus replication.

The human immunodeficiency virus type 1 (HIV-1) Rev protein is essential for the virus because it promotes nuclear export of alternatively processed mRNAs, and Rev is also linked to translation of viral mRNAs and genome encapsidation. Previously, the human DEAD-box helicase DDX1 was suggested to be involved in Rev functions, but this relationship is not well understood. Biochemical studies of DDX1 and its interactions with Rev and model RNA oligonucleotides were carried out to investigate the molecular basis for association of these components.

Single-molecule studies reveal that DEAD box protein DDX1 promotes oligomerization of HIV-1 Rev on the Rev response element.

Oligomeric assembly of Rev on the Rev response element (RRE) is essential for the nuclear export of unspliced and singly spliced human immunodeficiency virus type 1 viral mRNA transcripts. Several host factors, including the human DEAD box protein DDX1, are also known to be required for efficient Rev function. In this study, spontaneous assembly and dissociation of individual Rev-RRE complexes in the presence or absence of DDX1 were observed in real time via single-molecule total internal reflection fluorescence microscopy.

Protein structure and oligomerization are important for the formation of export-competent HIV-1 Rev-RRE complexes.

The translation of the unspliced and partially spliced viral mRNAs that encode the late, structural proteins of HIV-1 depends on the viral-protein Rev. Oligomeric binding of Rev to the Rev response element (RRE) in these mRNAs promotes their export from the nucleus and thus controls their expression. Here, we compared the effects of hydrophobic to hydrophilic mutations within the oligomerization domain of Rev using assays for oligomeric RNA binding, protein structure, and export from the nucleus.

Evidence for conformational flexibility in the Tat-TAR recognition motif of cyclin T1.

Cyclin T1 (CycT1) is a cellular transcription elongation factor that also participates in Tat-mediated activation of several lentiviral promoters. In human immunodeficiency virus (HIV), CycT1 is required for Tat to bind tightly to TAR and interacts in the ternary complex via its Tat-TAR recognition motif (TRM). In the related bovine immunodeficiency virus (BIV), Tat recognizes its cognate TAR element with high affinity and specificity in the absence of CycT1.