Gene and information diversity in eukaryotes

Reiteration frequency of procollagen genes in the guinea pig genome. Collagen genes are not amplified during granuloma fibroblasts differentiation

Procollagen mRNA was purified from collagen synthesizing polysomes obtained from an experimental guinea pig granuloma, and iodinated in vitro. The procollagen 125I-labelled mRNA was hibridized with granuloma and liver guinea pig DNA in vast DNA excess conditions. A Cot 1/2 800-900 mol . s . 1-1 for both tissues was obtained from the hybridization curves. With these results, we could suggest the existence of 11-13 procollagen genes per haploid genome. By the analysis of the hybridization data it was possible to infer that there is no genomic amplification in tissues highly specialized in the synthesis of collagen such as granuloma.

Genetic determination of antibody specificity. Gene translocation and fusion, the molecular basis for the differentiation of the antibody-producing cell

The best system for the study of cell differentiation is a cell which in its differentiated state differs only by one product. This is the case in the immune system. The undifferentiated, but omnipotent stem cell differentiates into a committed B cell which produces only one type of specific antibody out of a million different, genetically fixed possibilities. Gene translocation and fusion is the basis of this differentiation process.

Differential inhibitory effect of 5-fluorouridine on RNA labelling in dipteran salivary gland cells

In Chironomus salivary glands, 5-fluorouridine inhibits labelling of ribosomal RNA. The drug does not prevent labelling of other types of RNA- like heterodisperse messenger-like RNA, 75-S RNA of Balbiani ring origin and 4-S RNA, which furthermore are exported to cytoplasm. The potential use of this drug for the study of RNA metabolism in insect salivary glands can be compared with the use of low doses of actinomycin D in cultured mammalian cells.

The repetition frequency of DNA in Balbiani ring 2 of Chironomus thummi

The RNA of Balbiani ring BR2 of polytene chromosomes from Chironomus thummi salivary glands was microisolated and reassociated in the presence of an excess of total larval DNA. BR2 RNA reacts as a single component with a C0t 1/2 of 8.6. Ribosomal precursor RNA from microisolated nucleoli reassociates under identical conditions with a C0t 1/2 of 12.3. These C0t 1/2-values suggest repetition frequencies in the range of 35 and 50 for ribosomal DNA and Balbiani ring 2 DNA, respectively. The data presented here favour the view that the gene for BR2 RNA of C. thummi is internally repeated and contains only one type of DNA sequence.

The transcripts of Balbiani rings from Chironomus thummi. Giant RNA molecules with messenger characteristics

Experimental results on the transcription of Balbiani rings BR 1 and BR 2 of Chironomus thummi salivary gland chromosomes are presented. The DNA of Balbiani ring 2, which is the most active puff in larvae, is transcribed into large RNA molecules of about 22 X 10(6) D which resist degradation by heating, formamide or urea treatment. The asymmetrical distribution of electrophoretic profiles of BR 2 RNA and the appearence of a symmetrical BR RNA peak in the nucleoplasm suggest the synthesis of (mainly) one RNA fraction in BR 2. The gel electrophoretic patterns of BR 1 RNA are, on the other hand, characterized by the appearance of two main fractions of high molecular weight RNA, one of which corresponds in molecular weight (about 22 X 10(6) D) to BR 2 RNA. The second RNA fraction is significantly smaller in molecular size (molecular weight: about 10 X 10(6) D) and, like the 22 X 10(6) D RNA fractions of the two Balbiani rings, resistant against heating in 8 M urea. Binding to poly (U) sepharose of a significant part of Balbiani ring RNA suggests the existence of poly (A) and/or oligo (A) sequences in the Balbiani ring RNA. -- In situ hybridization of BR RNA to the salivary gland chromosomes reveals accumulation of silver grains over the Balbiani ring regions only and demonstrates the restriction of BR DNA sequences to the corresponding Balbiani ring.

Localization of 5 S RNA genes in Chirnomus tentans

The genes for 5 S RNA in Chironomus tentans have been located to region 2A of chromosome II by cytological hybridization. RNA from individual chromosomes, nuclear sap and nucleoli of salivary gland cells hybridized with the identified 5 S RNA genes in region 2A of chromosome II. The results suggest a common origin of 5 S RNA in these different nuclear compartments.