PCR with primers containing 5 0 -GC-clamp and 5 0 -M13 Sequences for the 5 0 M13 and GC-clamp portion of the primers, as well as the gene-specific portion of the primers used in this investigation are listed in Supplementary  Table 1 . The M13f and GC-clamp sequence was added to the 5 0 end of forward and reverse gene-specific primers respectively, or vice versa. Twenty microliter PCR reactions were performed from genomic DNA with final concentrations of reagents as follows: 1X JumpStart TM buffer (Sigma), 0.2 mM each dNTP, 0.2 mM forward and reverse primer, 1X JumpStart TM Taq polymerase (Sigma). PCR cycling was done on a Perkin Elmer 9600 PCR machine. The cycling conditions were: 948C, 90 s; (948C, 20 s/658C, 20 s/688C, 1 min) Â 10 cycles, with annealing temperature decreasing 18C/cycle, touch-down PCR; (948C, 20 s/558C, 20 s/688C, 1 min) Â 30 cycles; 688C, 5 min. This PCR program was linked to a program for denaturation and re-annealing of the PCR product over 10 min.