cDNA sequence and structure of a gene encoding trout testis high‐mobility‐group‐1 protein

Abstract

Perchloric acid extraction of trout testis nuclei revealed the presence of two large high‐mobility‐group (HMG) proteins, HMG‐T1 and HMG‐T2. The sequence of a complete cDNA (1407 bp) for trout testis HMG‐1 protein (referred as to HMG‐T1) has been determined. The deduced HMG‐T1 protein contains 203 amino acids with more than 86% similarity to mammalian HMG‐1 proteins. A single‐sized mRNA for HMG‐T1 has been detected by Northern‐blot analysis consistent with the size derived from the HMG‐T1 cDNA. Amplification of human and trout genomic DNAs by polymerase chain reaction using primers specific for trout and human HMG‐1 cDNAs revealed that unlike the human genome, which contains predominantly intronless HMG‐1 sequences, intronless HMG‐T1 sequences were not found in the fish genome. Southern‐blot analysis suggested that the trout testis HMG‐1 gene is encoded by at least two sequences with high similarity. A gene encoding HMG‐T1 protein has been isolated from a trout testis genomic library and by PCR of trout genomic DNA (3879 bp); The trout testis HMG‐1 gene is organized into five exons (four exons corresponding to the protein‐coding region) and its exon/intron boundaries are identical to those of the human HMG‐2 gene [Shirakawa, H. & Yoshida, M. (1992). J. Biol. Chem. 267, 6641–6645] suggesting the evolution of HMG‐1 and HMG‐2 genes from a common ancestor. Copyright © 1994, Wiley Blackwell. All rights reserved