Further characterization of the c-mos transcript and its cell cycle specific expression in NIH3T3 cells

The mouse c-mos proto-oncogene is primarily expressed in germ cells. Our previous studies demonstrated c-mos RNA expression in mouse somatic cells, with the highest level present in the G₂ phase of the cell cycle. We have identified the transcription start site of this G₂ specific c-mos transcript to be located about 1580 bp upstream from the open reading frame based on RT-PCR and RNase protection experiments. Upstream sequences containing this transcription start site directed highest expression of the luciferase reporter gene in M phase of the cell cycle. These results suggest that c-mos transcripts are produced in G₂ phase and that c-Mos protein albeit at extremely low levels would accumulate in M phase.