Methanobacterium thermoautotrophicum ⌬H, isolated in 1971 from sewage sludge in Urbana, Ill. (72), is a lithoautotrophic, thermophilic archaeon that grows at temperatures ranging from 40 to 70°C and optimally at 65°C. M. thermoautotrophicum conserves energy by using H 2 to reduce CO 2 to CH 4 and synthesizes all of its cellular components from these same gaseous substrates plus N 2 or NH 4 ϩ and inorganic salts, but despite this impressive biosynthetic capacity, M. thermoautotrophicum ⌬H and related strains have very small genomes (ϳ1.7 Ϯ 0.2 Mb [57,58]). M. thermoautotrophicum ⌬H, Marburg, and Winter are the foci of many methanogenesis, archaeal physiology, and molecular biology investigations, and M. thermoautotrophicum ⌬H was chosen as a representative of this group for genome sequencing. These thermophilic methanogens have mesophilic and hyperthermophilic relatives, Methanobacterium formicicum and Methanothermus fervidus, respectively, so that comparisons can be made of homologous

We compare the complexity and organization of the G protein c~ subunit multigene family in the vertebrate genomes of mammals and the Japanese puffer fish Fugu rubripes. Fourteen Fugu G~ genes were identified of the 16 genes characterized previously in mammals, including Fugu genes from the four classes of alpha subunits Gs, Gi, Gq, and G12. Fugu and mammalian GoL coding sequences are highly homologous, and the intron/exon structure of the fish and mammalian orthologs is identical throughout the coding regions. A novel GoL gene, Gc~pl, was also identified in Fugu rubripes and two other species of puffer fish. The complete sequence of Gnaz and the tandemly duplicated genes Gnai2 and Gnarl were obtained from a Fugu genomic cosmid library.introns in the puffer fish GoL genes lacked repeat DNA sequences, other than simple sequence length repeats, and most introns were significantly shorter in Fugu than in mammalian orthologs. The compact genome of puffer fish provides a unique vertebrate model for characterizing multigene families and identifying novel genes directly from genomic DNA by PCR amplification with degenerate primers. The fact that Fugu encodes most, if not all, of the G protein alpha subunits identified in mammals strongly supports Fugu as a model organism for vertebrate genome research.

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