ORGANIZATION OF XENOPUS HISTONE GENE VARIANTS WITHIN CLUSTERS AND THEIR TRANSCRIPTIONAL EXPRESSION

Using previously cloned Xenopus nucleosomal core histone genes as hybridization probes, a genomic DNA library of X. laevis was screened for histone gene clusters. From over 200 histone-gene containing clones identified, 36 were selected as possibly containing H1 histone genes by hybridization to a probe derived from a sea urchin H1 histone gene. These 36 clones were further analyzed by hybrid-selected translation for the definitive presence of H1 histone genes. The genes for 3 different H1 histone variants were found: H1A, H1B and H1C. Mapping of the histone genes within each clone showed that at least 3 different gene arrangements can occur within a cluster and that the type of H1 histone variant present in a cluster may be related to the cluster type. S1-mapping experiments indicated that histone genes found in different cluster-types can be expressed in oocytes. The H1 gene found in 1 cluster-type was expressed in at least 3 different cell-types: oocytes, gastrula-stage embryos and erythroblasts.