IDENTIFICATION OF 2 RNA-BINDING PROTEINS IN BALBIANI RING PREMESSENGER RIBONUCLEOPROTEIN GRANULES AND PRESENCE OF THESE PROTEINS IN SPECIFIC SUBSETS OF HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN-PARTICLES

Balbiani ring (BR) granules are premessenger ribonucleoprotein particl es (RNPs) generated in giant chromosomal puffs, the BRs, in the larval salivary glands of the dipteran Chironomus tentans, Monoclonal antibo dies were raised against nuclear proteins collected on a single-strand ed-DNA-agarose affinity column, and two of them were used to identify RNA-binding proteins in BR granules, First, in Western blots (immunobl ots), one of the antibodies recognized a 36-kDa protein and the other recognized a 45-kDa protein. Second, both antibodies bound to the BRs in immunocytological experiments, It was shown in cross-linking experi ments that the two proteins are associated with heterogeneous nuclear RNP (hnRNP) complexes extracted from C. tentans nuclei, By immunoelect ron microscopy of isolated and partly unfolded BR RNPs, it was specifi cally demonstrated that the BR granules contain the two proteins and, in addition, that both proteins are distributed frequently along the R NP fiber of the particles, Thus, the 36- and 45-kDa proteins are likel y to be abundant, RNA-binding proteins in the BR particles, To elucida te to what extent the two proteins are also present in other hnRNPs, w e studied the binding of the antibodies to chromosomal puffs in genera l, It was observed that many puffs in addition to the BRs harbor the t wo proteins, but there are also puffs containing only one of the compo nents, either the 36- or the 45-kDa protein, We conclude that the two proteins are not randomly bound to all hnRNPs but that each of them se ems to be linked to a specific subset of the particles.