FREQUENCY AND DISTRIBUTION OF DNA UPTAKE SIGNAL SEQUENCES IN THE HAEMOPHILUS-INFLUENZAE RD GENOME

The naturally transformable, Gram-negative bacterium Haemophilus influ enzae Rd preferentially takes up DNA of its own species by recognizing a 9-base pair sequence, 5'-AAGTGCGGT, carried in multiple copies in i ts chromosome. With the availability of the complete genome sequence, 1465 copies of the 9-base pair uptake site have been identified. Align ment of these sites unexpectedly reveals an extended consensus region of 29 base pairs containing the core 9-base pair region and two downst ream 6- base pair A/T-rich regions, each spaced about one helix turn a part. Seventeen percent of the sites are in inverted repeat pairs, man y of which are located downstream to gene termini and are capable of f orming stem-loop structures in messenger RNA that might function as si gnals for transcription termination.