Sf. Porcella et al., BORRELIA-BURGDORFERI SUPERCOILED PLASMIDS ENCODE MULTICOPY TANDEM OPEN READING FRAMES AND A LIPOPROTEIN GENE FAMILY, Journal of bacteriology, 178(11), 1996, pp. 3293-3307
DNA sequencing and Southern blot analyses of a Borrelia burgdorferi DN
A fragment encoding a signal sequence led to the discovery of a geneti
c locus, designated 2.9, which appears to be present in at least seven
copies in virulent B. burgdorferi 297. DNA sequence analysis of these
regions revealed that each 2.9 locus contained an operon of four gene
s (ABCD) and open reading frames designated rep(+) (positive strand) a
nd rep(-) (negative strand) which encoded multiple repeat moths. Downs
tream of the rep(+) gene(s) in six of the completely cloned and sequen
ced 2.9 loci also were lipoprotein (LP) genes possessing highly simila
r signal sequences but encoding variable mature polypeptides. The lipo
proteins could be separated into two classes on the basis of hydrophil
icity profiles, sequence similarities, and reactivity with specific an
tibodies. The 2.9 loci were localized to two (20- and 30-kb) supercoil
ed plasmids in B. burgdorferi 297. Northern (RNA) blot analysis establ
ished that the 2.9 ABCD operon was only minimally expressed, whereas t
he rep(-) gene(s) and at least three of the seven LP genes were expres
sed by B. burgdorferi in vitro. A single putative promoter element was
identified by RNA primer extension analysis upstream of the ABCD oper
on, whereas a number of potential promoter regions existed upstream of
the LP genes. The combined data indicate that the ABCD operon, rep(+)
and rep(-) genes, and LP genes are separately transcribed during in v
itro growth. The 2.9 loci possess a repetitiveness, diversity, and com
plexity not previously described for B. burgdorferi; differential expr
ession of these genes may facilitate the spirochete's ability to survi
ve in diverse host environments.