FIGURE 3.

Increased trans-splicing rates upon addition of hnRNP I are observed at low temperatures but not at 55°C. The influence of hnRNP I on trans-splicing was investigated at 55°C and at 25°C. The labeling of the bands is identical to Figure 2 and increase of the splice-product G-I1 was used as read-out for measuring the splicing reaction. At 55°C the presence of hnRNP I did not further stimulate trans-splicing (compare the first set of reactions with the second set). The third set of trans-splicing reactions at 55°C shows splicing in the presence of protein storage buffer (prot. b.), which slightly inhibited the splicing reaction (i.e., formation of G-I1) and almost completely abolished exon ligation. At 25°C splicing was hardly observed but strongly enhanced in the presence of hnRNP I (compare fourth and fifth sets of splicing reactions).