Promoter sequences required for transcription of Xenopus laevis histone genes in injected frog oocyte nuclei

Elements regulating differential activity of chicken histone H1 gene promoters

The chicken genome contains six closely related histone H1 genes, each of which encodes a different H1 protein. The four common regulatory elements previously identified in H1 histone promoters are very similar in sequence and location in all chicken H1 genes, which gives rise to the question of how the six H1 variants are expressed at significantly different levels. Transient transfections of reporter gene transcriptional fusions indicate that approximately 200 bp of each promoter is sufficient to generate the observed spectrum of H1 promoter activity. The differences in H1 promoter-driven expression are shown to be explained by the relative activity of the previously characterized G box region and that of a novel element found between CCAAT and TATA that we have termed differential upstream sequence (Dus). Gel shift analysis indicated that the primary nuclear binding protein to the G box is one or more avian homologues of the Sp1 transcription factor. The Dus region binds multiple nuclear proteins, one of which is the recently described IBR/IBF factor. The differential affinities of the G box and Dus sequences of the H1 promoters for their respective nuclear binding factors correlate well with their relative promoter activities.

Molecular characterization and cytogenetic analysis of highly repeated DNAs of lake trout, Salvelinus namaycush

The chromosomes of lake trout (Salvelinus namaycush) contain a considerable amount of heterochromatin located at the centromeres and/or telomeres of several chromosomes, including a sex-specific block located distally on the X chromosome. In order to investigate further the repetitive DNAs of lake trout, genomic DNA from a female was size fractionated (<600 bp) with the restriction endonuclease AluI and fragments were cloned into the bacteriophage M13. A total of 42 clones were isolated. Relative copy number of individual inserts within the lake trout genome was estimated by Southern analysis. Twelve clones were determined to be highly repetitive and were chosen for further investigation. Inserts of these clones contained sequences similar to the AluI/RsaI, EcoRI/DraI, DraI/BstEII, and MboI/BglII families reported from Arctic char (Salvelinus alpinus). The chromosomal location of several of these fragments was determined in lake trout by fluorescence in situ hybridization (FISH). Two related AluI/RsaI sequences (Type A, approximately 140 bp, and Type B,approximately 120 bp) showed differential hybridization. Type A hybridized to the centromeres of all metacentric as well as several acrocentric chromosomes. Type B hybridized to the centromeres of most acrocentric chromosomes. A sequence with homology to the EcoRI/DraI family hybridized to the centromeres of several acrocentric chromosomes. Sequences with partial similarity to the DraI/BstEII family hybridized to the major rDNA sites (nucleolar organizer regions, NORs) and several minor telomeric sites. The interstitial and telomeric heterochromatin of lake trout, including that of the X chromosome, appears to comprise sequences belonging to the MboI/BglII family.

Developmentally regulated expression of linker-histone variants in vertebrates

The identification of histone H1 variants in vertebrates suggests that these proteins may have specialized functions. During embryonic development, a correspondence between the expression of each of the linker-histone variants and the proliferative and transcriptional activity of embryonic cells can be observed. Analysis of the developmentally regulated expression of these variants leads to the subdivision of these variants into distinct classes. This subdivision may also provide insight into the significance of the differential expression of variants and the roles individual linker histones have in chromatin structure and function.