A study of mitochondrial and nuclear transcription with cloned cDNA probes. Changes in the relative abundance of mitochondrial transcripts after stimulation of quiescent mouse fibroblasts

Synthesis and stability of nuclear matrix proteins in resting and serum-stimulated Swiss 3T3 cells

The major [35S]methionine-radiolabeled nuclear matrix proteins of mouse 3T3 cells were isolated, and most of these were found to be similar in molecular weight, charge, and protease fingerprint to the nuclear matrix proteins of African green monkey kidney cells, which are found tightly bound to simian virus 40 chromosomes. These nuclear matrix proteins were found to be synthesized in quiescent and serum-stimulated cells and to be turned over slowly during pulse-chase experiments. In contrast, a 70-Kd (kilodalton) neutral protein identified as lamin a was found to be turned over rapidly, producing a 68-Kd protein with a similar isoelectric point. In addition, we observed a decrease in the amounts of two chromatin-bound matrix proteins and a relative increase in lamin a following labeling in the presence of 2 micrograms/ml actinomycin D. However, these effects do not appear to be a result of inhibition of transcription, since they were not observed with other inhibitors (alpha-amanitin and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole).

Characterization of a cDNA clone encoding murine mitogen-regulated protein: regulation of mRNA levels in mortal and immortal cell lines

Mitogen-regulated protein (MRP) is secreted by certain immortal murine cell lines (Swiss 3T3, BNL) stimulated with serum or particular growth factors. We have identified a cDNA clone that encodes part of the protein and have confirmed that MRP is closely related to, if not identical to, the prolactin-related protein designated proliferin. MRP is not produced by primary mouse embryo fibroblasts to nearly the same extent as it is produced by many immortal or transformed lines. Control of expression of this protein by growth factors is achieved both by regulating the extent of transcription and by regulating the processing of the protein.

Transcriptional regulation of two serum-induced RNAs in mouse fibroblasts: equivalence of one species to B2 repetitive elements

We obtained eight cDNA clones that define five genes whose expression (appearance of transcripts in the cytoplasm) is enhanced when quiescent mouse fibroblasts are stimulated with serum to divide. Two of these clones (designated 49C8 and 16C8) correspond to RNA species that are present in the cytoplasm of quiescent cells at very low levels. After serum stimulation, the level of 16C8 mRNA rose more rapidly than that of 49C8 RNA, reaching a maximum around 6 to 12 h. The data suggest that 49C8 and 16C8 RNAs are induced as a result of independent stimuli. Either fibroblast growth factor or 12-tetradecanoylphorbol-13-acetate alone could induce 16C8 expression almost as effectively as serum; in contrast, 49C8 was not efficiently induced by epidermal growth factor, fibroblast growth factor, insulin, or 12-tetradecanoylphorbol-13-acetate. Inhibitors of transcription and translation diminished the induction of 16C8, while 49C8 expression was sensitive to actinomycin D but not cycloheximide or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. In vitro transcription experiments with isolated nuclei revealed a peak in transcriptional activity of the 16C8 gene at around 3 h after serum stimulation. Sequence analysis of the 49C8 cDNA clone showed greater than 90% homology of a large portion to a consensus rodent B2 repetitive element.

A pBR322-derived vector for cloning blunt-ended cDNA: its use to detect molecular clones of low-abundance mRNAs

In place of the unique Pst I site in pBR322, we have engineered by GC tailing a unique Sma I site bracketed by Pst I sites. The resulting vector, pDE61, and an improved derivative with greater symmetry around the Sma I site, pDE613, have been used to clone blunt-ended duplex cDNA molecules in Escherichia coli in an efficient manner (5 X 10(5) clones from 1 microgram of double-stranded cDNA). When DNA is cloned into the Sma I site, the ability of both vectors to confer ampicillin resistance is lost. Evidence suggests that functional beta-lactamase is made only after the GC-rich sequence containing the Sma I site is deleted: an insert in the Sma I site prevents this. Libraries in either vector, with single or multiple inserts, can be used to generate amplified amounts of cloned heterogeneous cDNA for screening other "target" libraries in a non-homologous vector (e.g., a Bacillus subtilis vector) for cDNA clones of low-abundance mRNAs. Species as infrequent as 0.003% can be readily detected by colony hybridization.