Molecular structure and evolutionary origin of human cardiac muscle actin gene.

Abstract

Two recombinant phages that contain cardiac muscle actin gene were isolated from a human DNA library and their structures were determined. Restriction analysis indicates that both clones carry the same EcoRI 13-kilobase fragment where the coding sequence is mapped. The cloned DNA hybridized with polyadenylylated RNA from human fibroblasts, which directs the synthesis of cytoplasmic beta- and gamma-actin in vitro. However, sequence determination of the cloned DNA showed that the entire coding sequence perfectly matched the amino acid sequence of cardiac muscle actin. The initiation codon is followed by a cysteine codon that is not found at the amino-terminal site of any actin isoform, suggesting the necessity of post-translational processing for in vivo actin synthesis. There are five introns interrupting exons at codons 41/42, 150, 204, 267, and 327/328. Surprisingly, these intron locations are exactly the same as those of the rat skeletal muscle actin gene but different from those of nonmuscle beta-actin gene. Nucleotide sequences of all exon/intron boundaries agree with the G-T/A-G rule (G-T at the 5' and A-G at the 3' termini of each intron). The 3'-untranslated sequence has no homology to that of nonmuscle beta- or gamma-actin gene, but Southern blot hybridization has shown that this region has considerable homology to that of one of the other actin genes. These results indicate that the recombinant phages, which we have isolated, contain cardiac muscle actin gene and that cardiac muscle actin gene and skeletal muscle actin genes are derived from their ancestor gene at a relatively recent time in evolutionary development.

Isolation and characterization of full-length cDNA clones for human alpha-, beta-, and gamma-actin mRNAs: skeletal but not cytoplasmic actins have an amino-terminal cysteine that is subsequently removed.

“…We have demonstrated that the human fibroblast p-and y-actin genes do not encode a cysteine immediately following the MET initiation codon, unlike human a actin (this work) or cardiac actin (11). This result strongly suggests that two discrete actin gene types gave rise to the deuterostome actins, but this result also raises an unsettling evolutionary paradox.…”

“…In contrast, the demonstration of this encoded residue in chick a (6), rat a (29), human cardiac (11), and now human a actin (this work), in addition to all six Drosophila actin genes (7), raises the possibility that this residue is intimately involved in muscle actin gene expression. If this cysteine is post-translationally removed in all cases, as it clearly is in chicken (6) and mammals (26,29), then this residue may serve a regulatory rather than a structural role in actin expression.…”

“…Recently, sequence data of the chicken and rat a-actin genes and the human cardiac actin gene have also shown that the amino-terminal acidic residue is preceded in the primary translation product by a cysteine residue (6,11,29). Furthermore, two genes encoding cytoplasmiclike actins in the sea urchin have recently been shown similarly to have a cysteine codon at their amino termini (2) (W. Crain, personal communication).…”

Expression of CYP3A in the Human Liver — Evidence that the Shift between CYP3A7 and CYP3A4 Occurs Immediately After Birth

“…Hybridization and wash conditions have been previously described [21]. Membranes were stripped and reprobed with a p-actin probe [27]. Results were expressed as the CYP3A4 RNA/actin RNA ratio.…”

Structure, alternative splicing and chromosomal localization of the cystatin-related epididymal spermatogenic gene

“…These elements have the potential to adopt alternative DNA conformations that might direct the binding of transcription factors or other regulatory proteins to sites in the promoter [28].…”