SEQUENCE SURVEY OF THE GIARDIA-LAMBLIA GENOME

The parasitic protozoan Giardia lamblia represents one of the earliest diverging lineages in the evolutionary history of eukaryotic organism s as well as an important human pathogen. A representative sampling of gene sequences from this early diverging protozoan could provide insi ghts into genotypic and phenotypic innovations associated with the ori gin of eukaryotes. Currently, known giardial gene sequences are heavil y biased toward a few gene families, including variant surface protein s (VSPs), structural proteins, and ribosomal RNA genes. One-pass seque nces of Giardia genomic DNA were obtained using vector flanking primin g sequences on the ends of cosmids in two independent libraries. Compa risons of 2304 of these sequences against the GenBank(TM) database ide ntified 205 potential giardial genes with BLAST scores P(n) < 10(9). T hese coding regions encompass a wide range of metabolic, repair, and s ignaling enzymes, and include some genes not predicted by our current understanding of Giardia biochemistry. The efficiency of identificatio n of putative genes is consistent with earlier findings that coding re gions in the Giardia genome are densely packed and do not appear to co ntain introns. Our current results suggest that direct genome sequenci ng is an efficient method for identifying giardial genes for evolution ary and biochemical studies. (C) 1998 Elsevier Science B.V. All rights reserved.