Identification of two additional members of the tRNA isopentenyltransferase family in Physcomitrella patens

The Physcomitrella patens genome has seven genes apparently coding for the isopentenyltransferase type of tRNA-modifying enzyme, while other organisms have one or two. The predicted sequences have parts that differ significantly from other isopentenyltransferases. Only one of the seven (PpIPT1) has earlier been shown to be expressed. We now report expression of two more, PpIPT4 and PpIPT5. The cloned genes were able to functionally complement a yeast mutant lacking tRNA isopentenyltransferase. Sequencing showed they are related to the earlier studied PpIPT1. The sequences of the three differ mainly from each other in a tRNA-binding area and the 5'-end subcellular targeting motif area. This indicates that, after arising through gene duplication, they have evolved to enable partly different functions.