Organization and expression of cloned histone gene clusters fromXenopus laevisandX. boreolis

Abstract

We have isolated several clones containing Xenopus histone genes from genomic libraries of X. laevis and X. borealis DNA. Each genomic clone has been mapped and the positions of 26 histone genes in seven laevis clones and 5 histone genes in one borealis clone have been determined. In laevis, the histone gene clusters show considerable variation in gene order within a single individual. When the cloned DNAs were microinjected into the nucleus of Xenopus oocytes, expression of cloned genes at the transcriptional and translational level was readily detectable. Previously unknown histone variants were revealed by the microinjection experiments.

Histone gene number and organisation inXenopus: Xenopus borealishas a homogeneous major cluster

“…It now seems certain that in all X.laevis individuals there is an 8.9kb major Eco RI fragment (15,33,34) and this contains all 5 histone gene types (15,35). In our laboratory, double digestion of X.laevis genomic DNA with Bam HI and Eco RI produces a 4.1kb fragment containing both the HI and H4 genes.…”

“…There are now 21 genomic histone clones from X.laevis in the literature (15,16,33,34) and 14 of these are sufficiently well characterised to show the following:…”

“…However, the most frequent isolate from the library of Old et al (33) was an 8.6kb Eco RI fragment containing one copy of each of the 5 histone genes. This type of clone shares some of the characteristics of the major X.laevis cluster observed in Southern blot experiments.…”

Specific regulation of Xenopus chromosomal 5S rRNA gene transcription in vivo by histone H1.

“…We have not systematically attempted to decrease synthesis of H1B or H1C because they make up <5% of total histone HI at any time during Xenopus embryogenesis. Genes encoding all of these proteins have been cloned (Old et al 1982;Perry et al 1985).…”

“…The coding region of H1C (Old et al 1982) was cloned by PCR from X. laevis genomic DNA using the primers 5'-GAATTT-A_AGCTTCAAAGATGACAG-3' and 5'-GGAACTCTAGAGT-TACT'IXTTAGC-3'. This fragment was then subcloned into the XbaI and HindIII sites of pSP64pA (Promega).…”