Cloning and sequencing of cDNAs of the β-globin gene family in carp.

Abstract

A total blood cell cDNA library was constructed using a 3-year-old carp Cyprinus carpio. A β-globin cDNA (CβG1) was identified from the library by the polymerase chain reaction using a β-globin-specific primer deduced from the carp β-globin-A amino acid sequence. Also, five additional types of β-globin cDNAs (CβG2∼6) were isolated by colony hybridization using CβG1 as a probe. Sequence analysis revealed that these CβGs encoded 147 amino acids, and the deduced amino acid sequences showed high identity (89·1-95·2%) to previously reported carp β-globin amino acid sequences. The nucleotide sequences of the CβGs were very similar (identity 96·0-99·6%) and the expression levels of CβG1∼6 were 28·6, 28·6, 21·4, 14·3, 3·6 and 3·6% of the total number of cloned CβGs, respectively. Although the complete amino acid sequence identities between the CβGs and the β-globin of higher vertebrates were low, functionally important regions such as the α-βcontact region and haem contact region were well conserved. These data showed that, as in higher vertebrates, the adult carp has a multiple β-globin gene family (at least six members). However, transcripts encoding four types of peptides (CβG1 type, CβG2 and 3 type, CβG5 type, and CβG4 and 6 type) were expressed at relatively high levels, this being a unique character of the carp haemoglobin system.