The carbamoyl-phosphate synthase (CPS) enzyme in prokaryotes is a heterodimer, encoded by genes commonly called and . In most prokaryotes examined, these genes are separated by up to 24 bp and are cotranscribed. In and are also co-transcribed, but are separated by 682 bp. We have determined the complete DNA sequence of the and genes of strain CH811. (1125 bp) and (3237 bp) are similar in size and sequence to other prokaryotic CPS genes, however they are separated by an intervening sequence of 3290 bp which has no similarity to the intervening sequence between other CPS genes; furthermore, putative transcription terminators are found downstream of both and . Several neisserial repetitive sequences were identified within the 9 kb sequenced, as well as novel 120 and 150 bp repeats (designated RS6 and RS7, respectively) which were found within the intervening sequence between and . To determine whether the intervening sequence observed in CH811 was not unusual, the sequence between and was amplified by PCR from 30 isolates of . The intervening sequence was found to vary in size, from approximately 2:2 to 3:7 kb, although the and genes themselves did not vary in size in isolates with functional CPS enzyme. A similar large, variably sized intervening sequence was also found between the and genes of 12 isolates of and 18 commensal isolates comprising nine species. This unexpected organization of the CPS genes in is therefore widespread throughout the genus .


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