The messenger RNA sequences in growing and resting mouse fibroblasts

The sequences present in messenger RNA in resting and growing 3T6 cells have been examined. First, the abundance and complexity classes of mRNA in growing 3T6 were compared to those in other established cell lines. The overall complexities measured for mRNA from HeLa cells and the three mouse fibroblast lines, 3T6, SV-PY-3T3, and L, are qualitatively similar and correspond to approximately 10,000 sequences. The relative amount of the two major abundance classes and their complexities appear identical in the three mouse fibroblast lines despite their different histories. HeLa cell mRNA is significantly different both in the amount and the complexity of the two major classes. The complexity of the two mRNA classes appears the same in resting and growing 3T6, although there is a small difference in relative amounts. Cross hybridizing cDNA and mRNA from resting and growing cells shows that the majority of mRNA sequences are the same in the two states. However, cross hybridization after the common sequences are removed shows that about 3% of the mRNA in resting cells is not present in the growing state, while the opposite cross shows 3% of the mRNA in growing cells is not present in resting cells. These differences may result from alterations in gene expression which are related to the growth state of the cell.