Maturase and endonuclease functions depend on separate conserved domains of the bifunctional protein encoded by the group I intron aI4 alpha of yeast mitochondrial DNA.
Intron 4 alpha (aI4 alpha) of the yeast mitochondrial COXI gene is a mobile group I intron that contains a reading frame encoding both the homing endonuclease I-SceII and a latent maturase capable of splicing both aI4 alpha and the fourth intron of the cytochrome b (COB) gene (bI4). The aI4 alpha reading frame is a member of a large gene family recognized by the presence of related dodecapeptide sequence motifs called P1 and P2. In this study, missense mutations of P1 and P2 were placed in mitochondrial DNA by biolistic transformation. The effects of the mutations on intron mobility, endonuclease I-SceII activity and maturase function were tested. The mutations of P1 strongly affected mobility and endonuclease I-SceII activity, but had little or no effect on maturase function; mutations of P2 affected splicing but not mobility or endonuclease I-SceII activity. Surprisingly, the conditional (temperature-sensitive) mutations at P1 and P2 block one or the other function of the protein but not both. This study indicates that the two functions depend on separate domains of the intron-encoded protein.
Henke
R M
RM
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235-9038, USA.
Butow
R A
RA
Perlman
P S
PS
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D004251:DNA Transposable Elements; D004272:DNA, Mitochondrial / Q000235:genetics*; D015252:Deoxyribonucleases, Type II Site-Specific; D003576:Electron Transport Complex IV / Q000235:genetics; D004706:Endodeoxyribonucleases / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D008928:Mitochondria / Q000201:enzymology; D008969:Molecular Sequence Data; D005810:Multigene Family; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames / Q000235:genetics; D012326:RNA Splicing; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
D004251:DNA Transposable Elements; D004272:DNA, Mitochondrial; D029701:Saccharomyces cerevisiae Proteins; D003576:Electron Transport Complex IV; D004706:Endodeoxyribonucleases; C066166:AI4 protein, S cerevisiae; D015252:Deoxyribonucleases, Type II Site-Specific