Molecular Analysis of Bovine Actin Gene and Pseudogene Sequences: Expression of Nonmuscle and Striated Muscle Isoforms in Adult Tissues

Most studies on the tissue distribution of actin isoform transcripts have been done in small mammals such as rat and mouse. We have begun a characterization of the actin gene family in a large mammal, the bovine. The α skeletal gene was isolated, and an isoform-specific probe to the 3′ untranslated region of the transcript identified. This probe, in combination with isoform specific probes for α cardiac, β nonmuscle, and γ nonmuscle actins, was used to examine expression of nonmuscle and striated muscle actin gene transcription in different tissues. In contrast to other species so far examined, striated muscle isoforms were more strictly tissue specific, with virtually no α cardiac isoform transcripts detected in skeletal muscle and almost no α skeletal transcripts in cardiac tissue. The distribution of the β and γ nonmuscle actins was also unique in bovine compared to other species. A partial β-actin pseudogene, and the chromosomal DNA flanking one end of it, were also cloned and sequenced. This chromosomal site was found to be homologous to a viral integration site previously identified in simian virus 40 (SV40)-transformed rat cells, suggesting that this region of the chromosome may be a preferred target for insertion events.