MICROBIOLOGY. For the article “Yersinia pestis, the cause of plague, is a recently emerged clone of Yersinia pseudotuberculosis” by Mark Achtman, Kerstin Zurth, Giovanna Morelli, Gabriela Torrea, Annie Guiyoule, and Elisabeth Carniel, which appeared in number 24, November 23, 1999, of Proc. Natl. Acad. Sci. USA (96, 14043–14048), the authors note the following correction. In describing the homologies among sequences of housekeeping gene fragments from Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica, the thrA, trpE, and manB7 sequences reported from Y. enterocolitica were incorrect and are from residual Escherichia coli DNA contaminating the Taq polymerase used for PCR amplification. The thrA and trpE alleles now have been sequenced by using a combination strategy of inverse PCR and subcloning, and the correct sequences have been deposited in the GenBank database under the accession nos. AJ250241, AJ270409, and AJ288275-AJ288285. We have been unable to sequence the manB allele from strains formerly reported as possessing manB7 and have removed the GenBank entry AJ270447. As a result of these new data, several statements in the publication need correcting.

Seven different alleles of thrA and five alleles of trpE were found among the 13 strains of Y. enterocolitica that were tested (Table 1). Formerly, we concluded that thrA and trpE were homogeneous in Y. enterocolitica. Instead, the mean genetic distances between these alleles within Y. enterocolitica and between Y. pestis and Y. enterocolitica are comparable or slightly higher than those described previously (1) for glnA, tmk, or dmsA (Table 2). The data from these five genes allow estimating the date of separation between Y. pestis and Y. enterocolitica to be 42–187 million years. We have confirmed that the other sequences described previously are correct. None is related to E. coli sequences or to those of other bacteria with which we have worked. We also resequenced all six genes from 23 representative strains of Y. pestis and Y. pseudotuberculosis and did not find any differences from those reported previously. Thus, the conclusions regarding the relationships between Y. pestis and Y. pseudotuberculosis remain unchanged, as are the proposals for their evolutionary history.

Table 1.

Alleles of three gene fragments in Y. enterocolitica

IP number	thr A	trpE	manB
383	6	4	10
21349	9	4	10
21650	6	5	10
864	8	4
21699	8	4
134	8	4
885	8	4
24636	8	4
25963	12	9	9
21708	10	6
21506	11	6	9
Ye8081	7	8	8
WA	7	7	8

 IP number, Institut Pasteur strain designation. Empty cells indicate the lack of data. 

Table 2.

Mean percent pairwise differences at synonymous (% D_S) and nonsynonymous (% D_N) sites of three gene fragments

Gene (size)	Distance	enterocolitica (13)*	pe→ent
thrA (393 bp)	% DS	12.2 (0–40)	154 (144–176)
	% DN	0.3 (0–1)	1.5 (1.0–2.2)
trpE (351 bp)	% DS	3.7 (0–8.4)	146 (136–177)
	% DN	<0.06	3.0 (2.9–3.1)
manB (442 bp)	% DS	154 (0–289)	>100
	% DN	14 (0–24)	16 (13–20)

 pe, Y. pestis; ent, Y. enterocolitica. 

^*The number of strains is indicated in parentheses after the species designation.