CHICKEN ALPHA-ENOLASE BUT NOT BETA-ENOLASE HAS A SRC-DEPENDENT TYROSINE-PHOSPHORYLATION SITE - CDNA CLONING AND NUCLEOTIDE-SEQUENCE ANALYSIS

Chicken alpha- and beta-enolase cDNAs have been cloned and analyzed to reveal that alpha- but not beta-enolase has a Src-dependent phosphorylation site. The deduced amino acid sequence of the chicken alpha-enolase showed more than 90% homologies with those of other vertebrate alpha-enolases including amphibian (Xenopus laevis) alpha-like enolase. The chicken beta-enolase, on the other hand, shares 84-85% amino acid sequence homology with mammalian beta-enolases. These chicken enolases also showed more than 70% sequence identity with an insect (Drosophila melanogaster) enolase and around 60% with two yeast enolases. The amino acid sequence between residues 33 and 50 in chicken alpha-enolase coincided with the reported tryptic peptide sequence of rabbit beta-enolase, the tyrosine residue in which was phosphorylated in vitro by Rous-sarcoma-virus tyrosine kinase. The present finding suggested that the tyrosine residue at position 44 in chicken alpha-enolase is the phosphorylation site by the tyrosine kinase. In chicken beta-enolase, on the other hand, the corresponding tyrosine residue was found to be replaced with a histidine residue, in accordance with the previous observation that chicken beta-enolase was not phosphorylated in vivo or in vitro. Northern blot analysis indicated that alpha-enolase mRNA can be expressed in a wide range of chicken tissues, and that the gene expression switch from alpha- to beta-enolase occurs just after hatching in developing chicken muscle.