There are five sequences annotated as coding for APT or APT like 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Also, transcripts for APT4 are not detectable by RT-PCR analysis of leaf or flower RNA (Moffatt, unpublished data).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