Functional activity and developmental regulation of DdRBP1, a RNA binding protein in Dictyostelium discoideum

The ubiquitous nature of RNA chaperone proteins

RNA chaperones are ubiquitous and abundant proteins found in all living organisms and viruses, where they interact with various classes of RNA. These highly diverse families of nucleic acid-binding proteins possess activities enabling rapid and faithful RNA-RNA annealing, strand transfer, and exchange and RNA ribozyme-mediated cleavage under physiological conditions. RNA chaperones appear to be critical to functions as important as maintenance of chromosome ends, DNA transcription, preRNA export, splicing and modifications, and mRNA translation and degradation. Here we review some of the properties of RNA chaperones in RNA-RNA interactions that take place during cellular processes and retrovirus replication. Examples of cellular and viral proteins are dicussed vis à vis the relationships between RNA chaperone activities in vitro and functions. In this new "genomic era" we discuss the possible use of small RNA chaperones to improve the synthesis of cDNA libraries for use in large screening reactions using DNA chips.

Identification of STKA-dependent genes in Dictyostelium discoideum

During culmination of Dictyostelium aggregates, prespore and prestalk cells undergo terminal differentiation to form spores and a cellular stalk. Disruption of the cell-fate gene stkA leads to a phenotype in which all the cells destined to become spores end up as stalk cells. 'Stalky' mutants express normal levels of prespore cell transcripts but fail to produce the culmination-stage spore transcript spiA. The stkA gene encodes a putative GATA-type transcription factor (STKA). In order to identify possible downstream targets of STKA we used the technique of mRNA differential display and isolated four cDNA fragments that hybridise to mRNAs present during the later stages of development. All four gene tags were cloned and sequenced. mRNAs represented by these four sequence tags do not accumulate during culmination of 'stalky' cells and therefore must be specific to the spore pathway. By screening a cDNA library, longer cDNAs for all four were cloned and sequenced. Three of these contained complete protein-coding regions while only a partial cDNA was recovered for the fourth. One of the corresponding proteins has significant homology to a surface zinc metalloproteinase (GP63) of the protozoan parasite Leishmania, while another is closely related to a human pre-RNA binding protein (hnRNP R).