PubMed Health⌕ Search

Biomedical subjects

F J Lara

Publications and source records attributed to F J Lara.

36 records · Page 2Linked to original sources
PubMed1976

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. Studies of the product under the incubation conditions show that the system allows the synthesis of high-molecular weight RNA, beside a low molecular weight peak which may comprise pre-4S and 5S RNAs. Autoradiographic studies carried out in the presence or absence of the toxin alpha-amanitin showed that micronucleoli contain products of RNA polymerase type I activity (ribosomal RNA) and that the DNA puffs are engaged in alpha-amanitin sensitive RNA synthesis and thus are sites of polymerase type II activity.

Amanitins↗
PubMed1975

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.--Injection of actinomycin D at different times after ecdysone injection abolished the higher incorporation rate at the amplifying regions within 15 hours after the injection. However, the percentage of nuclei incorporating 3H-TdR and the frequency of the two labeling patterns remained essentially the same when RNA synthesis was inhibited. Only the over-all rate of 3H-TdR incorporation seemed to be reduced.--These data suggest that in the DNA puff regions the rate of DNA chain elongation is higher when amplification occurs than during a normal replication cycle. It, further, seems that the higher rate during amplification is dependent upon de novo RNA synthesis.

Animals↗
PubMed1975

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. The data indicate the existence of stable messengers in the salivary glands.

Animals↗
PubMed1975

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'.

Animals↗
PubMed1975

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. It consists of the following steps. (1) The molecules in an RNA sample are first separated according to their molecular weight by electrophoresis in agarose, at low ionic strength. 2. The molecules thus seperated are then submitted to a second electrophoresis in 'binding buffer' in a direction perpendicular to the first one. In the course of this electrophoresis the poly(A)-containing RNA species are seperated from other RNA species as they bind to a poly(U)-containing glass-fibre filter which is placed across the electrophoresis path. The method was used to determine the electrophoretic profile of Rhynchosciara salivary-gland messenger RNA. It was found that the population of messenger RNA in the gland is dominated by forms moving as 18 and 158 S peaks, but there is also polydisperse RNA with slower mobility.

Animals↗
PubMed1974

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. americana rRNA. The percentage of hybridization was found to be higher in tissues with low polyteny than in tissues with high polyteny, suggesting a relationship between the amount of rDNA and the tissue polyteny. This could be explained by under-replication of ribosomal cistrons in polytene cells, such as those from the salivary gland. Only slight tissue-dependent changes in the percentages of hybridization can be observed in heterologous hybridization using Xenopus laevis rRNA. The possibility that these experiments could not detect differences in the amount of ribosomal cistrons among tissues is discussed. The female:male ratio for the percentages of hybridization in the salivary gland of R. americana agrees with the results obtained by in situ hybridization experiments (16, 17) which have shown that the rRNA cistrons are distributed among chromosomes other than chromosome X.

Adipose Tissue↗