THE MOUSE HISTONE H1 GENES - GENE ORGANIZATION AND DIFFERENTIAL REGULATION

There are six mouse histone H1 genes present in the histone gene clust er on mouse chromosome 13. These genes encode five histone H1 variants expressed in somatic cells, H1a to H1e, and the testis-specific H1t h istone. Two of the genes that have not been assigned previously to the five somatic H1 subtypes have been identified as encoding the H1b and H1d subtypes. Three of the H1 genes, H1a, H1c and H1t, are present on an 80 kb segment of DNA that contains nine core histone genes. Two ot hers, H1d and H1e, are present in a second patch, while the H1b gene i s at least 500 kb away in a patch containing 14 core histone genes. Th e histone H1 genes are differentially expressed. All five genes for th e somatic histone H1 proteins are expressed in exponentially growing c ells. However, the levels of H1a, M1b and H1d mRNAs are greatly reduce d in cells that are terminally differentiated or arrested in G0, while the H1c and H1e mRNAs continue to be expressed. In addition to the ma jor RNA that ends at the stem-loop, the H1c gene expresses a longer, p olyadenylated mRNA in differentiated cells, although in varying amount s. None of the other histone H1 genes encodes detectable amounts of po lyadenylated mRNAs. (C) 1997 Academic Press Limited.