Discovery of Analog Enzymes in Thiamin Biosynthesis by Anticorrelation

Enrique Morett1, J. Korbel2, K. Emmanuvel Rajan1, G. Saab-Rincon1, L. Olvera1, M. Olvera1, B. Snel2, S. Schmidt2, and P. Bork2., 1Instituto de of Biotecnologia, Universidad Nacional Autonoma de Mexico, AP 510-3, Cuernavaca Mor. 62250.Mexico; 2 European Molecular Biology Laboratory, Meyerhofstrasse 1. Heidelberg 69117. Germany.

Prediction of gene function is one of the most challenging tasks in genomic science when there is no clear sequence similarity to annotated genes. Here we present a new method denominated Anticorrelation of Gene Presence to predict gene function. This method assumes that analog proteins, ie proteins that perform the same function but arose by independent evolution, normally are mutually exclusive in the genomes. We analyzed the thiamin (vitamin B1) biosynthesis pathway in the completely sequenced microorganisms to validate our method. We identified several different ORFs which do not have homology to any known thi gene from Escherichia coli which might be involved in thiamin biosynthesis. We have cloned some of these genes from Thermotoga maritima, Saccharomyces cerevisiae, Bacillus subtilis, and Rhizobium etli and used them to complement the thiamin deficiency of thiC, thiE, thiG and thiH mutant strain generated by precise gene deletion. Our results demonstrated that seven of these genes indeed participate in thiamin biosynthesis. and gene displacement has occurred often in thiamin biosynthesis. These data demonstrate that the anticorrelation method is robust and useful in predicting gene function.