The principal route for adenine recycling is mediated by adenine phosophoribosyl-transferase which converts adenine and PRPP to AMP and PPi.
There are five sequences annotated as coding for APT or APTlike enzymes in the Arabidopsis genome. These have
been designated APT1-5 .
At present there is evidence for the expression of only APT1, 2 and 3. No ESTs specific for APT4 or 5 have been
identified and those that are listed in their Genbank records are more similar to the other APT sequences.
Also, transcripts for APT4 are not detectable by RT-PCR analysis of leaf or flower RNA (Moffatt, unpublished data).
It should be noted that APT5 is less than 12% identical to APT1 at the amino acid level, raising the possibility that APT5 may utilize a substrate other than adenine, in vivo