Variation of Chargaff differences (%) and purine/pyrimidine (R/Y) ratios along the first 20 kb of the genomic sequence of the thermophileM. jannaschii. A 1-kb sequence window was moved in steps of 0.1 kb, and base compositions were determined in each window. From these, Chargaff differences (○ for the W bases; ◼ for the S bases), and R/Y ratios (continuous line), were calculated. Data points are located at the center of each window. The locations of putative ORFs are shown as boxes (open for transcription to the left; shaded for transcription to the right; orientations are also marked by horizontal arrows below each box). Although most ORFs correspond to hypothetical proteins, some tentatively identified ORFs have been labeled: (aspB1) Aspartate aminotransferase; (activ) activator of 2-hydroxyglutaryl-CoA dehydratase; (formate dehyd.) α and β subunits of formate dehydrogenase; (glutar) β subunit of 2-hydroxyglutaryl-CoA dehydratase; (pyruvate decarb.) phosphonopyruvate decarboxylase; transposase; (gatB) Asp-tRNA amidotransferase, subunit B.