Reiteration frequency of the gene for tissue-specific histone H5 in the chicken genome

Histone gene number and organisation in Xenopus: Xenopus borealis has a homogeneous major cluster

Using a Xenopus laevis H4 cDNA clone as a probe we have determined that the numbers of H4 histone genes in Xenopus laevis and Xenopus borealis are approximately the same. These numbers are dependent on the hybridization stringency and we measure about 90 H4 genes per haploid genome after a 60 degrees C wash in 3 X SSC. Using histone probes from both Xenopus and sea urchin we have studied the genomic organization of histone genes in these two species. In all of the X.borealis individuals analyzed about 70% of the histone genes were present in a very homogeneous major cluster. These genes are present in the order H1, H2B, H2A, H4 and H3, and the minimum length of the repeated unit is 16kb. In contrast, the histone gene clusters in X.laevis showed considerable sequence variation. However two major cluster types with different gene orders seem to be present in most individuals. The differences in histone gene organization seen in species of Xenopus suggest that even in closely related vertebrates the major histone gene clusters are quite fluid structures in evolutionary terms.

The chicken H5 gene is unlinked to core and H1 histone genes

An H5 cDNA clone was used to select H5 genomal recombinants from a chicken Charon 4A library. DNA sequence analysis shows that the H5 gene contains no introns. Putative 5' promoter elements and a 3' polyadenylation site are present within the 1.8 kb of DNA examined. Analysis of 41 kb of DNA surrounding the H5 gene shows that it is not closely linked to either H1 or core histone genes.Images

Is histone H5 present in mammals?

An extraction procedure for histone H5 for chicken erythrocytes described in the literature has been applied to mouse spleen. The SDS polyacrylamide gel electrophoresis pattern of the resulting protein preparation revealed the presence of a component with the mobility of the marked chicken erythrocyte H5. Additionally the preparation has been characterized using antiserum raised against purified chicken H5. The presumptive mouse spleen H5 preparation gave visible precipitation lines with the anti-H5 chicken-antiserum. The combined electrophoretic and immunological evidence suggests the presence of histone H5 in mammalian tissue.

Histone genes are clustered but not tandemly repeated in the chicken genome

The recombinant chicken DNA library was screened for histone genes by using pSp17, a recombinant sea urchin DNA probe containing the H2a and H3 genes of Strongylocentrotus purpuratus. Three of the isolated lambda recombinants have been analyzed by restriction enzyme mapping and Southern blotting; one histone H3 gene-encoding recombinant was further analyzed by DNA sequence determination. These studies reveal that the chicken histone genes are not tandemly reiterated, but that, at the least, several histone genes are physically closely linked in a nonrepetitive arrangement within the chicken genome. The evolutionary implications of this arrangement versus that seen in Drosophila and sea urchins is discussed.

Histone H5 messenger RNA is polyadenylated

In most known systems, histone mRNA lacks the poly(A) sequence at the 3' end of the molecule typical of most mRNAs. Furthermore, the synthesis of histones, unlike that of most proteins, is tightly coupled to DNA synthesis. Nevertheless, histone synthesis occurs in amphibian oocytes in the absence of DNA synthesis. Moreover, it has recently been found that in amphibian oocytes most of the histone mRNA is polyadenylated, and the polyadenylate is probably removed during maturation of the oocyte. Histone H5, an H1-like tissue-specific histone occurring only in nucleated erythrocytes, is also atypical in that it is synthesised in the absence of DNA synthesis during maturation of the red blood cells. We report here that H5 mRNA is polyadenylated.

Histone genes are clustered with a 15-kilobase repeat in the chicken genome

Histone mRNA isolated from 5-day-old chick embryos has been used as a template for complementary DNA (cDNA) synthesis. The resultant cDNA, after removal of sequences complementary to rRNA, was used to detect histone genes in adult chicken genomal DNA. Hybridisation data indicate that the histone genes are repeated about 10-fold in the chicken genome. Restriction endonuclease analysis reveals some sequence heterogeneity in these genes. However, the results show that chicken histone genes are clustered with a basic repeat unit of 15 kilobases.

Terminal riboadenylate transferase from Escherichia coli. Characterization and application

Catalytic properties of terminal riboadenylate transferase from Escherichia coli and the products of the enzymic reaction were investigated. The kinetic analysis revealed that the reaction obeys the sequential ordered bi-bi mechanism. The application of conditions elaborated in this study resulted in the synthesis of products of defined size and efficient primer utilization. The tRNA(rA)n obtained was a good template for the synthesis of complementary DNA with reverse transcriptase.