Showing papers by "Alan T. Bankier published in 1980"

Different pattern of codon recognition by mammalian mitochondrial tRNAs.

Abstract: Analysis of an almost complete mammalian mitochondrial DNA sequence has identified 23 possible tRNA genes and we speculate here that these are sufficient to translate all the codons of the mitochondrial genetic code. This number is much smaller than the minimum of 31 required by the wobble hypothesis. For each of the eight genetic code boxes with four codons for one amino acid we find a single specific tRNA gene with T in the first (wobble) position of the anticodon. We suggest that these tRNAs with U in the wobble position can recognize all four codons in these genetic code boxes either by a "two out of three" base interaction or by U.N wobble.

Sequence of Mammalian Mitochondrial DNA

Abstract: The human mitochondrial (mt) genome consists of a closed circular duplex DNA approximately 10 x 106 daltons and has been the most intensely studied animal mt genetic system. The positions of the origin of replication of H strand synthesis (Crews et al. 1979), the 12S and 16S ribosomal RNA genes (Robberson et al. 1972) and 19 tRNA genes (Angerer et al. 1976) have been located on the genetic map shown in Figure 1. A number of discrete products of mitochondrial protein synthesis have been demonstrated and three of them identified as subunits 1, 2 and 3 of the cytochrome oxidase complex (Hare et al. 1980). In comparison with other mito-systems, genes for up to four subunits of the ATPase complex, one of the cytochrome bc1 complex and possibly for a ribosomal protein would be expected to be present (see review by Borst 1977). Both strands are thought to be completely transcribed symmetrically from a point near the origin of the H strand synthesis (Aloni and Attardi 1971; Murphy et al. 1975). These transcripts are then processed to give the rRNAs, the tRNAs and a number of polyadenylated but not capped mRNAs (Attardi et al. 1979). Both the L and H strands have been shown to be coding with the L strand containing the sense sequence of the rRNA genes, most of the tRNA genes and most of the stable polyadenylated mRNAs.

Different pattern ofcodonrecognition bymammalian mitochondrial tRNAs

Abstract: Analysis ofanalmost cornplete mammalian mitochondrial DNAsequence hasidentifiemd23 possible tRNA genes andwespeculate here that these aresufficient totranslate all thecodons ofthemitochondrial genetic code. This number ismuchsmaller than theminimum of31required bythewobble hypothesis. Foreachoftheeight genetic codeboxes with four codons foroneaminoacid wefind asingle specific tRNAgene with Tinthefirst (wobble) position oftheanticodon. Wesuggest that these tRNAswith Uinthewobble position canrecognize all four codons inthese genetic codeboxes either bya"twoout ofthree" base interaction orbyUN wobble. Mitochondrial DNAcodes foranumber oftRNAsaswell as ribosomal RNAsandseveral respiratory proteins. Nineteen tRNAshavebeenmapped (byhybridization) onthehuman mitochondrial genome (1, 2)andmitochondrial tRNAs specific for all amino acids except L-proline, glutamine, histidine, and asparagine have beenidentified bycharging experiments (1). Similar studies onratliver mitochondrial tRNAshave identified all species except those forglutamine andhistidine (3). As- suming that all mammalian mitochondria codeforthesame complement oftRNAs, these studies bring thenumber of mammalian mitochondrial tRNAs sofar identified to21,which includes twoserine tRNAs, twoleucine tRNAs, atRNAmet, and atRNAMet. Studies onpurified ratliver mitochondria and cytoplasmic tRNAshavefailed toshowanyimportation of cytoplasmic tRNAsinto themitochondrion (3). Themito- chondrial tRNAshaddifferent chromatographic properties on RPC-5columns andpolyacrylamide gelelectrophoresis from their cytoplasmic counterparts, andnomitochondrial tRNAs hybridized tonuclear DNA. Thesmall number ofmammalian mitochondrial tRNAsand thelack ofanyimported cytoplasmic tRNAsraises theproblem ofhowthese tRNAsrecognize all possible codons inmito- chondrial protein synthesis. Onthebasis ofthewobble hy- pothesis (4), aminimumof32tRNAsareneeded toread all possible codons ofthe"universal" genetic code. Recent studies have established that humanandbovine mitochondria have a different genetic code inthat UGAistryptophan andnotter- mination andAUAismethionine andnotisoleucine (ref. 5; I.G.Y., unpublished results). Thus, aminimumof31tRNAs would beneeded. However, recently anumber ofinvitro experiments have indicated that thewobble hypothesis might notapply andthat insomecases thethird (wobble) position ofthecodon hasno discriminatory function. Mitra etal.(6) studied theincorpo- ration ofvaline inaninvitro protein-synthesizing