TABLE 1.

Distribution of Rag motifs in different chromosome regions^a

Region (min)	No. of Rag motifs		No. of anti-Rags in seriesb of:
	Total	Anti	2	3	4	5	6
0-10	151	34	4
10-20	175	30	3	2
20-30	184	23
30-40c	175	6
40-50	153	23	3				1
50-60	159	25	5	1
60-70	146	39	5			1
70-80	149	36	11
80-90d	143	43	5	2	2
90-100	135	29	7	1
Total	1,570	288	43	6	2	1	1

^aOn 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.

^bSee 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.

^cdif at 34 min.

^doriC at 84 min.