A cDNA was isolated from the human heart library. This cDNA variant was produced by the deletion of 176 bases at the 5' end of human RecQL gene, presumably by an alternative mRNA splicing. The cDNA contains two open reading frames and so may encode two isoforms of human RECQL. The first isoform is a 105 amino acid protein with the first 53 N-terminal amino acids identical to the known sequence of RECQL protein and followed by 52 amino acids introduced by in-frame premature stop codon. The second isoform is a 537 amino acid protein that has the same sequence as the published human RECQL helicase, except the first 112 amino acids at the N-terminal end were absent. The possible roles of both of these proteins are discussed. (C) 2002 Elsevier Science (USA). All rights reserved.