Role of Protein Methylation in Halobacterium halobium Phototaxis.
Annual progress rept. 1 Oct 1991-31 Aug 1992
TEXAS UNIV MEDICAL SCHOOL AT SAN ANTONIO
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In earlier work on this project a methylated membrane protein of 97KDa M sub r. was suggested on the basis of mutant analysis to transduce signals from the phototaxis receptor sensory rhodopsin I to the flagellar motor in H. halobium Spudich et al, Proc. Natl. Acad. Sci. USA 867746-7750, 1989. In this period we competed the cloning of the proposed transducer protein gene based on partial and protein sequences from the isolated protein, the complete gene sequence analysis of the encoded primary structure. The gene ends immediately at the initiator codon of the sopl gene which encodes the sensory rhodopsin I apoprotein. Putative promotor elements are located in an AT-rich region upstream of the gene. Comparison of the translated nucleotide sequence with N-terminal sequence of the purified protein shows the protein is synthesized without a processed leader peptide and the N-terminal methionine is removed in the mature protein. The deduced protein sequence predicts two transmembrane helices near the N-terminal which would anchor the protein to the membrane. Beyond this hydrophobic region of 46 residues, the remainder of the protein 535 amino acid residues total is hydrophilic. The C-terminal 270 residues contain a region homologous to the signalling domains of eubacterial transducers e.g. Escherichia coli Tsr protein, flanked by two regions homologous to the methylation domains of the transducer family. The predicted protein structure differs from that of E. coli Tsr in that it does not have an extramembraneous receptor binding domain, but instead has a more extended cytoplasmic region.
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