The nucleotide sequence of a 12 . 5 kbp segment of the left arm of chromosome IV is described. Five open reading frames (ORFs) longer than 100 amino acids were detected, all of which are completely confined to the 12 . 5 kbp region. Two ORFs (D1271 and D1286) correspond to previously sequenced genes (PPH22 and VMA1 or TFP1, respectively). ORF D1298 shows the characteristics of alpha-isopropylmalate and homocitrate synthase genes and is similar to the nifV gene of Azotobacter vinelandii. Two more ORFs have no apparent homologue in the data libraries. Conversely, two smaller ORFs of 25 and 85 amino acids encoding the ribosomal protein YL41A and an ATPase inhibitor, respectively, were detected. Although a substantial part of the 125 kbp fragment apparently lacks protein-coding characteristics, no other elements, such as tRNA genes or transposons, were found.