Variant FLP recombinase proteins with different activity levels have been isolated. Most fly constructs appear to express one of two FLP variants (FLPD5 or FLPG5, see below), however, other variants also exist. We do not know the FLP allele present in most Bloomington stocks. The table below shows stocks where we do know the FLP variant expressed.

Known variants:

• FLPD5 and FLPG5 - FLP with either glycine (FLPG5) or aspartic acid (FLPD5) at amino acid 5. The FLPD5 version has more than tenfold higher activity than the FLPG5 version according to Nern et al. 2011.
• FLPL with aspartic acid at amino acid 5 (D5) and leucine at amino acid 70. It appears to have intermediate activity between the D5 and G5 variants.
• FLPL2 with glycine at amino acid position 5 (G5) and leucine at position 70.
• FLPo is a mouse codon optimized FLP. We have no information about its relative efficiency.

In the following stocks, some FLP variants are tagged with a PEST sequence to shorten their half-lives. FLP expression can also be driven by different numbers of UAS repeats.

David Bilder sequenced two X-linked P{hsFLP} insertions and reports they carry the D5 variant. Given the ambiguities surrounding the identities of most hs-FLP insertions on the X (for details see our note on X-linked hs-FLP insertions), we list here only those P{hsFLP} stocks for which we are reasonably certain of their origin.