Differential nuclear localization and nuclear matrix association of the splicing factors PSF and PTB

A monoclonal antibody raised against nuclear matrix proteins detected a pro tein of basic pi in human nuclear matrix protein samples of various cellula r origin. The ubiquitously occurring (common) nuclear matrix protein was id entified as splicing factor PSF (PTB associated splicing factor). The inter action between the splicing factors PSF and PTB/hnRNP I was confirmed by co -immunoprecipitation from nuclear salt extracts. However, the nuclear local ization of PSF and PTB and their distribution in subnuclear fractions diffe red markedly. Isolated nuclear matrices contained the bulk of PSF, but only minor amounts of PTB. In confocal microscopy both proteins appeared in spe ckles, the majority of which did not co-localize. Removing a large fraction of the soluble PTB structures by salt extraction revealed some colocalizat ion of the more stable PTB fraction with PSF. These PTB/PSF complexes as we ll as the observed PSF-PTB interaction may reflect the previously reported presence of PTB and PSF in spliceosomal complexes during RNA processing. Th e present data, however, point to different cellular distribution and nucle ar matrix association of the majority of PSF and PTB. (C) 2000 Wiley-Liss, Inc.