An alternative calculation based solely on average gene size is provided by: P = 1-(1-x/G)n where P is the probability of the T-DNA inserting in a given target of size x in a genome of size G Selleckchem Proteasome inhibitor with n the total number of T-DNA insertion mutants [35]. Assuming an average gene size of 2000 nucleotides, this calculation estimates a library of nearly 60,000 mutants would be required for a 95% probability of obtaining at least one insertion mutant

in any given gene. Such a mutant bank would require 300 pools with an average pool size of 200 and PCR screening could be easily performed using three 96-well plates. Although our current collection of 4000 mutants is inadequate for complete genome coverage, it was sufficient to demonstrate proof-of-concept through identification and recovery of a mutant at the CBP1 locus. Isolation of a cbp1 insertion mutant Detection of a T-DNA insertion in CBP1 As no cbp1 mutant exists in the NAm 2 background despite numerous attempts with allelic replacement, we screened our NAm 2 mutant BMN 673 ic50 bank for T-DNA insertions that disrupt the CBP1 gene. The Cbp1 protein was the first virulence factor demonstrated for Histoplasma through deletion of the encoding gene in a Panama class strain of Histoplasma [20]. Two CBP1 gene-specific primers were designed at the 3′ end of the CBP1 coding region and were oriented towards the 5′ end of the gene. As the T-DNA element

could insert with either the T-DNA left border or the right border oriented towards the 3′ end of the CBP1 gene, we screened each mutant pool by PCR Tobramycin with RB3 or with LB6 primers in combination with the CBP1-21 gene-specific primer. While PCR reactions with the LB6 + CBP1-21 primer set did not produce any positive PCR products with any of the templates (data not shown), reactions with RB3 and CBP1-21 primers produced amplicons in two different pools (Figure 3A, lanes

2 and 12). Low abundance bands less than 100 bp are likely primer dimers or residual RNA from the template nucleic acids and were thus not considered. A nested PCR reaction was performed on the RB3-set of reactions (Figure 3B). The PCR product from pool 2 did not re-amplify in the nested PCR reaction suggesting that this product was a non-specific amplicon. Alternatively, the pool may indeed harbor an insertion of T-DNA sequence in the CBP1 locus but the T-DNA element could be truncated and the nested RB primer-binding site lost resulting in failure to amplify in the nested PCR. The nested PCR reaction from pool 12 produced a very prominent, approximately 800 bp amplicon consistent with an insertion in the DNA upstream of the CBP1 coding region (Figure 3B, lane 12). Sequencing of this amplicon confirmed insertion of the T-DNA in the CBP1 promoter and localized the insertion 234 base pairs upstream of the CBP1 start codon (Figure 3C).