FUNCTIONAL-CHARACTERISTICS OF THE MAIZE RNA-BINDING PROTEIN MA16

The maize RNA-binding protein MA16 is a non-ribosomal nucleolar protei n widely distributed in different maize tissues. We have previously sh own that the MA16 protein binds preferentially to guanosine- and uridi ne-rich sequences. As a step towards the identification of specific ta rgets with which MA16 interacts within the cell, we investigated the R NA-binding affinities and several other aspects of the protein by usin g binding assays and immunochemistry. The MA16 protein showed a wide s pectrum of RNA-binding activities with lower affinities to several RNA s that was salt and heparin-sensitive indicative of electrostatic inte ractions, and higher affinities to particular RNAs including rRNA and translatable mRNA sequences. Among the RNAs found associated with MA16 protein was that encoding MA 16 itself. This observation raises the p ossibility that MA16 gene expression could be self-regulated. Immunopr ecipitation studies showed that in vivo MA16 was phosphorylated and th at MA16 interacts with RNAs through complex association with several p roteins. These results suggest that both phosphorylation and interacti on with other proteins may be involved in determining RNA-binding spec ificities of MA16 in the cell.