Arolla, Switzerland

Date:
1980
Reference:
PP/CRI/E/1/28/12
Catalogue details

Licence: In copyright

Credit: Arolla, Switzerland. Source: Wellcome Collection.

    33/102
    posr -transcriptional regulation in the cytoplasm o f chick eryt ii rodlasts H-T. Itnaizumi-Scherrer , K. Maundrel], 0. Civelli and K. Scherrer I.R.B.M. PARIS Duck erythroblast messenger RNA was isolated from polyribo somes and from repressed mRNP free in the cytoplasm ; these two compartments contain 88 S and 12 % respectively of the polyadenylated mRNA. After oligo(dT) cellulose chromatography, both mRNA populations were either transcribed into cDNA by RNA-dependent DNA-polymerase, or translated in RNase treated reticulocyte lysates. The kinetic complexity of the polyribosomal cDNA hybridizing back to its template shows the presence of 211 mRNA species in three abundancy classes : a and ß globin mRNA (70 % in mass) are represented by about 3 800 copies/cell, 7 mRNA by about 90 copies/cell and 202 mRNA by 2 copies/cell. The repressed free cytoplasmic mRNP contains 1 400 different mRNAs also in three abundancy classes. The a and ß globin mRNA (44 % of mass) are represented by about 285 copies, there are 19 mRNA with 7 copies, and 1380 mRNA represented by less than one copy per cell. These data indicate that about 1 200 mRNA species are not represented at all in polyribosomal mRNA. Heterologous cross- hybridization of cDNA transcribed from free mRNP message with poly ribosomal mRNA suggests that the intermediate frequency mRNA classes are very differently represented in the two compartments. The qualitative difference of these mRNA populations is also demonstrated by two-dimensional electrofocussing and electrophoresis of the products of in vitro translation. Among the almost fully repress ed mRNAs we find e.g. the mRNA for the polyribosomal poly(A)-binding protein ; the repression of this mRNA may be one of the factors lead ing to the arrest of protein synthesis in late reticulocytes. We conclude that the repressed mRNA population is at last seven fold more complex than the translated one. Individual equilibria of activity exist for each mRNA which allow full translation, and thus expression of some genes, but also condition full repression at post- transcriptional levçl of a majority of activated genes. These data are discussed as examples in support of the Cascade Regulation scheme. S.l MAPPING OF VI RAL mRNA IN SV40 T RANSFO RMED RAT CELLS J. 1MUERT - 1NSERM MARSEILLE Abstract not received