Although this is an attractive model, 738 the fact that a deletion encompassing the high affinity hnRNP A1 binding site in the 3'UTR is 739 able to replicate and direct normal synthesis of subgenomic mRNAs makes the PTB-hnRNP A1 740 association less likely to have a crucial role in leader-body rejoining (Goebel et al., 2007) , 741 although the possibility that other members of the hnRNP family could substitute for hnRNP A1 742 remains a possibility (see section 5 for a discussion of this).