Cloning and sequence analysis of cDNA for rat spleen thymosin beta 4.

Molecular cloning of a cDNA has established the sequence of the translated portion of the mRNA for rat spleen thymosin beta 4. The presence of a methionyl initiator codon immediately preceding the codon for the first seryl residue of mature thymosin beta 4 is consistent with previous results indicating the absence of a signal peptide in the product translated in vitro from rat spleen mRNA. The cDNA sequence analysis also established the presence of two terminator codons immediately following the codon for the COOH-terminal seryl residue. Thymosin beta 4 is thus synthesized as a 5100-dalton peptide containing 44 amino acid residues. Removal of the initiator methionyl residue and acetylation of the NH2-terminal serine residue would yield mature thymosin beta 4 containing 43 amino acids. The absence of a signal peptide makes it unlikely that thymosin beta 4 is a secreted peptide.