TABLE 1.

Distribution of Rag motifs in different chromosome regionsa

Region (min)No. of Rag motifsNo. of anti-Rags in seriesb of:
TotalAnti23456
0-10151344
10-201753032
20-3018423
30-40c1756
40-501532331
50-601592551
60-701463951
70-801493611
80-90d14343522
90-1001352971
Total1,570288436211
  • a On the sequence of the E. coli chromosome (7), a Rag motif is found every 3.3 kb on average, and the average skew is 82.4%. The skew shift is neat at dif (Fig. 1) but is less clear at oriC (not shown). For about 640 kb, 360 to the left of dif and 280 to the right (26.5 to 40.5 min on the genetic map), polarization is extreme; this region harbors 230 Rags with only 7 (3%) in antiorientation. The occurrence of anti-Rag series outside the highly polarized region is compatible with random distribution: a blind drawing of 1,340 Rags among an infinite population of iso-Rag and anti-Rag in the same proportions as in the chromosome (outside the highly polarized TER region), yields numbers of anti-Rag series close to 41 doublets, 9 triplets, and 3 tetrads. This is not very different from the actual distribution, except that the probability of occurrence of the series of 5 and 6 is low.

  • b See Materials and Methods for discussion of the nomenclature. By “series” is meant a succession of anti-Rags uninterupted by an iso-Rag in the sequence of the region considered.

  • c dif at 34 min.

  • d oriC at 84 min.