Open AccessPurification, cDNA cloning and Northern‐blot analysis of mitochondrial chaperonin 60 from pumpkin cotyledons
Author(s) -
TSUGEKI Ryuji,
MORI Hitoshi,
NISHIMURA Mikio
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb17309.x
Subject(s) - biology , chaperonin , complementary dna , biochemistry , southern blot , microbiology and biotechnology , amino acid , peptide sequence , cdna library , groel , transit peptide , open reading frame , hsp60 , heat shock protein , escherichia coli , gene , plastid , chloroplast , hsp70
Two different cDNA clones, pMCPN60‐1 and pMCPN60‐2, encoding the mitochondrial homologues of chaperonin 60 (Cpn60) were isolated from a cDNA library of germinating pumpkin cotyledons by use of mixtures of synthetic oligonucleotides based on the N‐terminal amino acid sequence of the protein. Determination of the complete nucleotide sequences of the two cDNA revealed that pMCPN60‐1 and pMCPN60‐2 each contain one open reading frame that encodes a protein of 575 amino acids with molecular masses of 61052 Da and 61127 Da, respectively. The deduced amino acid sequences of the two polypeptides include a 32‐residue N‐terminal putative mitochondrial presequence attached to the mature polypeptides, and they are 95.3% identical. From a comparison of deduced amino acid sequences with other Cpn60, it appears that the mature polypeptides of pumpkin mitochondrial Cpn60 are 44–59% identical to the other Cpn60, namely, GroEL of Escherichia coli , the 60‐kDa heat‐shock protein (Hsp60) of mitochondria in the yeast Saccharomyces cerevisiae , P1 protein of mammalian mitochondria and the Ribulose‐1,5‐bisphosphate carboxylase/oxygenase subunit‐binding proteins α and β of plastids in higher plants. Genomic Southern‐blot analysis identified at least two copies of the gene for mitochondrial Cpn60 in the pumpkin genome. The levels of mRNA for mitochondrial Cpn60 in cotyledons, hooks and hypocotyls of pumpkin seedlings increased in response to heat stress, as deduced from Northern‐blot analysis, indicating that pumpkin mitochondrial Cpn60 is a heat‐induced stress protein.