Transient repression of erythromycin formation in Streptomyces erythraeus.

The effect of a D-glucose on growth and erythromycin production by Streptomyces erythraeus was investigated. D-Glucose stimulated growth and caused a strong but temporary suppression of antibiotic formation. Maximum specific suppression of erythromycin formation occurred at a carbohydrate concentration of 20 mg ml-1.

Gene amplification in Rhynchosciara salivary gland chromosomes.

Late in the fourth larval instar, several regions of the Rhynchosciara americana salivary gland chromosomes undergo "DNA puffing." We have constructed a library of cloned cDNAs synthesized from poly(A)+RNA isolated from salivary glands during the period of development when the DNA puffs are active. From this library we have studied clones representative of three genes active during this period but not active at earlier developmental periods of the gland.

Cloning and characterization of the ribosomal RNA genes of Rhynchosciara americana.

The ribosomal RNA genes (rDNA) of Rhynchosciara americana were analysed using Southern transfers of DNA cleaved with EcoRI, HindIII, BamHI and PstI. The results show that the rDNA is heterogeneous in structure. Following digestion with EcoRI and hybridization to rRNA three bands corresponding to fragments of 9.

Immunofluorescent characterization of DNA . RNA hybrids on polytene chromosomes of Trichosia pubescens (Diptera, sciaridae).

We have studied the distribution of DNA X RNA hybrids on polytene chromosomes with the aid of a goat antibody against DNA X RNA hybrids using the immunofluorescence technique. Fixed polytene chromosomes of the sciarid Trichosia pubescens (Diptera) show distinct, stage-specific labelling patterns throughout larval development. Controls for the staining procedure - including preincubation with hybrid-specific endoribonuclease H - prove that DNA X RNA hybrids are present on fixed chromosomes.

The transcript from a DNA puff of Rhynchosciara and its migration to the cytoplasm.

Electrophoretic analysis of 3H-RNA obtained from the proximal sections of Rhynchosciara salivary glands at two distinct developmental periods, one characterized by the presence and the other by the absence of the giant B-2 DNA puff, revealed that the appearance of a 14S poly(A)+ RNA is correlated with the opening of this puff. That this RNA species is transcribed from this puff is indicated by the fact that it is found in RNA extracted from B-2 puffs obtained by microdissection. This confirmed by the specific hybridization of the 14S poly(A)+ RNA to the B-2 locus.

Distribution of repetitive DNA sequences in the polytene chromosomes of Rhynchosciara americana.

The distribution of fast, intermediate and slow renaturing fractions of Rhynchosciara americana DNA was examined in the polytene salivary gland chromosomes by in situ hybridization. Heterochromatic areas readily hybridized but hybrid formation in the euchromatin depended more on the repetitiveness of the RNA probe.

In vitro transcription by isolated nuclei of Rhynchosciara americana salivary glands. Characteristics of incorporation and inhibition by alpha-amanitin.

A method for the isolation of polytene nuclei from salivary glands cells of the Diptera Rhynchosciara americana is described. The stage-specific morphological pattern of the chromosome is maintained during the isolation. The isolated nuclei show two distinct RNA polymerase activities, namely I and II, characterized on the basis of ionic requirements and alpha-amanitin sensitivity.

A micro-method for the assay of polyadenylate-containing ribonucleic acid by gel electrophoresis.

A micro-method for the determination of the electrophoretic profile of the various poly(A)-containing RNA species in a RNA sample was developed. The method is simple to carry out and allows for great reproducibility. It combines the resolving power of electrophoresis in agarose with the specificity of binding of poly(A) to poly(U)-containing glass-fibre filters.

Histone synthesis in Rhynchosciara salivary glands. I. Site and timing of synthesis.

The site of histone synthesis was studied in polytene cells of the salivary glands of the Rhynchosciara americana (Diptera). It was found that, as is the case in non-polytene systems, these proteins are synthesized in the cytoplasm in a class of light polysomes which contain 3-4 ribosomes. This class of polyribosomes is most active at about 5 days before pupation when the nuclei are most active in DNA synthesis and the chromosomes of the gland show many open 'DNA puffs'.

Isolation and characterization of polyribosomes from the salivary glands of Rhynchosciara americana.

Polyribosomes were obtained in high yield from Rhynchosciara salivary glands by a method which uses the non-ionic detergent Nonidet P 40, in moderate salt buffer and DTT as RNase inhibitor. The polysomal profiles from glands of animals which have just started to spin the communal cocoon are slightly but consistently different from those obtained from about 5 day older animals, in which DNA puffs were open in the salivary gland chromosomes. The heaviest polyribosomes which could be detected by either radioactive uridine or amino acid incorporation have 8 to 9 ribosomes.

RNA synthesis: a requirement for hormone-induced DNA amplification in Rhynchosciara americana.

Injection of beta-ecdysone into mid fourth instar larvae of Rhynchosciara americana induced within 23-28 hours after injection a rise in the percentage of 3H-thymidine (3H-TdR) incorporating nuclei in salivary gland region S1 from about 10-20% in the controls to 80-90% in the injected larvae. The 3H-TdR incorporating nuclei displayed a weak continuous labeling pattern or a band-labeling pattern with grains over the vast majority of the bands. The majority of nuclei with a band labeling pattern displayed DNA amplification at the DNA-puff regions.

Under-replication of ribosomal cistrons in polytene chromosomes of Rhynchosciara.

DNA preparations obtained from several tissues of Rhynchosciara americana and two related species, R. milleri and R. papaveroi, were hybridized to R.