The nucleotide sequence of the rat β-actin gene was determined. The gene codes for a protein identical to the bovine β–actin. It has a large intron in the 5’ untranslated region 6 nucleotides upstream from the initiator ATG, and 4 Introns 1n the coding region at codons specifying amino acids 41/42, 121/122, 267, and 327/328. Unlike the skeletal muscle actin gene and many other actin genes, the 6-act1n gene lacks the codon for Cys between the Initiator ATG and the codon for the N-terminal amino acid of the mature protein.

The usage of synonymous codons 1n the β–actin gene is nonrandom, and is similar to that in the rat skeletal muscle and other vertebrate actin genes, but differs from the codon usage in yeast and soybean actin genes.