Actin Coding Research Articles

Isolation and characterization of human actin genes.

We have utilized cloned actin genes from Drosophila melanogaster and from chicken to isolate 12 actin gene fragments from a human DNA library. Each of these 12 clones was shown to contain actin coding regions by its ability to selectively hybridize to human actin mRNA as assayed by in vitro translation. The translation product was judged to be actin on the basis of its comigration with authentic actins when electrophoresed on one- and two-dimensional NaDodSO4/polyacrylamide gels and on the basis of its partial proteolysis products. Determination of the sizes and order of the fragments generated by restriction endonuclease digestion of each of these recombinant phages allows us to conclude that they are nonallelic and are from nonoverlapping regions of the genome. We have used these cloned human actin genes and the Drosophila and chicken actin gene clones to show that the human genome contains 25-30 EcoRI fragments homologous to actin genes and that, among three nonconsanguineous individuals tested, none of these fragments exhibit length or restriction-site polymorphism.

Putative actin genes in the macronucleus of Oxytricha fallax.

Previous work has shown that the macronuclear DNA of the hypotrichous ciliate Oxytricha fallax is arranged as short achromosomal pieces, 22 to 0.5 kilobase pairs (kb) in length. Micronuclear DNA has a typical chromosomal organization. Macronuclear DNA is derived from micronuclear DNA through a process of polytene chromosome fragmentation with a resultant decrease in DNA sequence complexity. Three putative actin genes have been identified in macronuclear DNA by using a cloned yeast actin gene as a hybridization probe. A restriction fragment of the yeast gene containing both actin coding and noncoding DNA hybridizes strongly to two macronuclear DNA pieces, 1.6 and 1.4 kb in length, and weakly to a 1.2-kb piece. The entire 1.6-kb piece has been cloned in plasmid pBR322 and the resulting recombinant plasmid has been designated pOfACT(1.6). The 1.6-kb pOfACT(1.6) insert hybridizes only to those restriction fragments of the yeast actin gene containing actin coding sequences. When hybridized to macronuclear DNA under conditions that allow the yeast probe to hybridize to all three macronuclear pieces, the pOfACT(1.6) insert hybridizes only to the 1.6-kb piece. Under less stringent conditions the insert also hybridizes to the 1.4-kb piece, but it shows no hybridization to the 1.2-kb DNA. The three macronuclear pieces homologous to the yeast actin gene thus differ in sequence and are interpreted as a related family of actin genes. Each of these pieces could accommodate an actin coding sequence, which in yeast, Dictyostelium discoideum, and Drosophila melanogaster is 1.1 kb, and an additional 0.1-0.5 kb of noncoding DNA.

Cloning of sea urchin actin gene sequences for use in studying the regulation of actin gene transcription.

In order to investigate the regulation of actin gene transcription during early sea urchin development, a specific hybridization probe for actin sequences is required. Such a probe was produced by cloning cDNA transcribed from a sea urchin poly(A)-containing mRNA preparation enriched for actin message. Double-stranded DNA was ligated into the BamHI restriction site of plasmid pBR322, and the resulting hybrid molecules were used to transform the Escherichia coli strain ML100. After preliminary screening of bacterial colonies by antibiotic sensitivity and hybridization back to the original cDNA, clones containing sea urchin DNA were further characterized by a positive translation assay in which total sea urchin mRNA was hybridized to plasmid, and the hybridized message then was eluted and translated in a reticulocyte cell-free protein-synthesizing system. In this way, one clone (pSA38) was found to hybridize selectively to sea urchin mRNA coding for a protein of 43,000 daltons. This protein was identified as actin by three criteria: electrophoretic migration in two-dimensional polyacrylamide gels, affinity for DNase I, and peptide mapping. Restriction endonuclease and heteroduplex mapping of pSA38 indicate that it contains a 1.5-kilobase-pair insert and is therefore likely to contain a large portion of the actin coding sequence. By using pSA38 as a hybridization probe, it has been found that the level of actin-specific RNA sequences increases dramatically during early sea urchin development.