Quantitative analysis of histone H1 degrees protein synthesis in HTC cells

H1 degrees, a member of histone H1 family associated with cell growth arres t and differentiation, is barely expressed in most mammalian cells in cultu re. Depending on the cell type, serum deprivation or drugs, such as sodium butyrate, significantly increase H1 degrees mRNA level and H1 degrees prote in accumulates. However, probably because of a lack of a simple quantitativ e procedure, little is known about the relationship between H1 degrees mRNA content and its effective translation rate. Using a rat hepatoma cell line and sodium butyrate as a model system, we attempted to evaluate this in di fferent cellular conditions by measuring H1 degrees synthesis with a rapid quantitative procedure we described previously. We found that although the amount of H1 degrees mRNA rapidly increased and then stabilized under sodiu m butyrate treatment, its transcription was delayed and H1 degrees protein was synthesized in a progressive wave. Butyrate removal from cell culture c onfirmed that mRNA level and protein synthesis were independently regulated , and provided evidence that sodium butyrate would not directly target the translation apparatus. In contrast, during the S phase of the cell cycle, H 1 degrees gene transcription and protein synthesis were concomitantly activ ated. Taken together these data provide evidence that H1 degrees accumulati on results from an increase of its synthesis and that, depending on conditi ons, a cell exhibits a H1 degrees translation efficiency which may or may n ot reflect the mRNA level.