TABLE 2.

Primers used in this study

Primer	5′-to-3′ sequencea
Primer1a	AATCAGACCATGGTTGAAATTAATCCGG (NcoI)
Primer1b	CTCTTTCTCTCGAGCGTAGTCAAAGATACCCCCTAAG (XhoI)
Primer2a	TCACCCGGGAAACCAATTGTCCATATTGC (XmaI)
Primer3a	GTGTAGGCTGGAGCTGCTTC
Primer3b	TTAGCCCCCGGGCATATGAATATCCTCCTTAG (XmaI)
Primer4a	gagcgtggattgggtacaatcccgctcttatcaccgcaGTGTAGGCTGGAGCTGCTTC
Primer4b	cttcttccagacgctctttcttggcgtcgtagtcaaagatacc
pctrl1	CTGGCCATTTTAGCGTCATCTTCTC
pctrl2	AGACATCCGGCTGTTCCAGCTCGGCG

^aUnderlined nucleotides introduce the restriction sites as indicated in parentheses. Boldface indicates primer site 1 (10). Lowercase indicates parts homologous to prfB, used for recombination (H1 and H2 for Primer4a and Primer4b, respectively; see Fig. 1B).