The multigene histone family displays a number of fascinating properties; cell-cycle regulation, transcriptional and post- transcriptional control, coordinate regulation and differential gene expression of individual members within a family. The objectives of this proposal concern determination of the level of regulation of partially replication-dependent (PRD) to fully replication-dependent (FRD) histone gene switching during differentiation of murine erythroleukemia (MEL) cells. We will begin to identify the signals involved in this regulation. We propose several approaches to determine the extent to which transcriptional and post-transcriptional regulation are involved in histone gene switching. These approaches include: 1) Testing of PRD and FRD genes in DNA-dependent transcription extracts for differential changes in transcription efficiency. 2) Establishment of gene constructs which are regulated, after transformation, in a PRD or FRD manner. 3) Determination of the changes in transcription rates of individual histone genes during differentiation, using in vitro nuclear transcription. 4) Measurement of the half-life of different histone mRNAs during differentiation. We will then extend these approaches to map the signals involved in this regulation. The histones are known to be essential to the structural integrity of chromatin but their role, if any, in the regulation of gene expression is obscure. A better understanding of the histone gene switching which occurs during differentiation of the murine erythroleukemia cells may give some insight into the effect upon gene expression if such exists.
