The positions of the several sea urchin histone genes on the eukaryotic fragments of the chimeric plasmids pSp2 and pSp17 have been mapped relative to the Eco RI and Hind III restriction endonuclease ...sites on the plasmids. Two principal mapping methods using the electron microscope have been used: (a) the R-loop procedure and a new modification thereof to map the genes on duplex DNA; (b) the gene 32-ethidium bromide technique to visualize RNA-DNA hybrids on single strands of DNA. It is known that there are two histone genes, H3 and H2A, on pSp17. There are two Eco RI sites at the two junctions of the procaryotic segment with the eucaryotic segment on the plasmid. We show, by an electron microscope method, that for H2A, with a length of 0.52 kilobases (kb), one end of the gene is situated 0.02 to 0.03 kb from one RI site, and that there is a Hind III site within this gene at about 0.13 kb from the end phe other RI site of this plasmid. The H4 gene lies between H2B and H1. The ms the incubation temperature is raised up to a temperature just below that at which strand dissociation of the duplex DNA occurs.
We have analyzed the histone genes from the sea urchin Lytechinus pictus. Examination of native DNA from individuals reveals four major Eco RI restriction endonuclease histone gene DNA fragments ...which have been labeled A (6.0 kb), B (4.1 kb), C (3.1kb) and D (1.2 kb). The fragments A, B and C have been cloned into E. coli plasmids (pLpA, pLpB and pLpC). These histone gene fragments display length and sequence heterogeneity in different individuals. The plasmid pLpA contains the coding regions for H1, H4, H2B and H3 histones, and we determined that the DNA fragment D is tandem to A in native DNA and that it contains the H2A gene. The plasmids pLpB and pLpC contain the histone genes H2A-H1-H4 and H2B-H3, respectively, and together contain the sequences for the five major histones. Restriction analysis of native L. pictus DNA reveals that B and C are tandem to each other but not intermingled with the A--D-type repeat units, and are thus in separate clusters with a repeat length of 7.2 kb. Since the two cluster types do not segregate, they are not alleles. Hybridization of histone mRNA to exonuclease III-digested linear DNA demonstrated an identical polarity of the histone genes in the A--D- and B--C-type repeat units. This result revealed that the L. pictus histone genes have a polarity which is the same as other sea urchin histone genes examined to date--that is, 3' H1-H4-H2B-H3-H2A 5'. Restriction endonuclease cleavage patterns of the cloned segments indicate that considerable sequence heterogeneity exists between the two types of histone gene repeat units.
Tritium-labeled complementary RNA's to two cloned sea urchin DNA sequences, one coding for histones H1, H2B, and H4 and the other for H2A and H3, were hybridized in situ to high resolution human ...chromosomes. Evidence is presented showing that the histone genes in man are localized in bands q32-36 on the long arm of chromosome 7.
The DNA sequence of two cloned segments of the histone gene repeat unit of the sea urchin S. purpuratus has been determined. One sequence contains the contiguous H2B and H3 genes and their ...interdigitated spacer regions; the other comprises the H2A gene and flanking spacer sequences. Analysis of the coding regions reveals a methionine residue within the H2A protein. H2A, which generally lacks this amino acid, contains methionine only in a protein variant which is synthesized in early sea urchin embryogenesis. We thus conclude that the cloned DNA represents a set of genes which is active early in development. Codon selection is markedly skewed and similar for each of the three genes. The DNA sequences are co-linear with known histone protein sequences and-unlike several other eucaryotic genes-do not show any insertions in the coding regions. The spacer regions are relatively AT-rich although GC cluster are scattered throughout. Several short stretches of homology are found in regions both upstream and downstream from the protein coding segments. The conservation of these sequences and their location at analogous sites suggest that they are involved in gene transcription or in mRNA translation. No tandem or dispersed repeats were found, with the exception of the remarkable sequence having the structure located in the spacer between the H2A and H1 genes.
This paper describes briefly the BIONET National Computer Resource for Molecular Biology. This presentation is intended as information for scientists in molecular biology and related disciplines who ...require access to computational methods for sequence analysis. We describe the goals, and the service and research opportunities offered to the community by BIONET, the relationship of BIONET to other national and regional resources, our recent efforts toward distribution of the resource to BIONET Satellites, and procedures for investigators to gain access to the Resource.
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