The natural transformation system of the thermophilic bacteriumThermus thermophilus HB27 comprises at least 16 distinct competence proteins enco-ded by seven distinct loci. In this article, we present for the first time biochemical analyses of the Thermus thermophiluscompetence proteins PilMNOWQ and PilA4, and demonstrate that thepilMNOWQgenes are each essential for natural transformation.