Xenopus laevis histone genes: variant H1 genes are present in different clusters.

The Xenopus laevis histone genes have been isolated from a bacteriophage lambda library using a cloned cDNA probe to X. laevis H4 mRNA (pX1ch4). Their structural organization has been determined by restriction mapping, blot hybridization and hybridization selection and translation of Xenopus histone mRNAs. They are clustered and probably tandemly arranged but, in contrast to invertebrate histone genes (Kedes, 1979), there has been extensive sequence divergence in the spacer regions of the clusters. Also, the order of the genes within individual clusters is not conserved. We report the isolation of two variant histone H1 gene and find that the order of the nucleosomal core histone genes within a cluster containing an H1B gene is different from that found in two clusters containing the H1A gene.