Genetic analysis of functional domains within the drosophila LARK RNA-binding protein

LARK is an essential Drosophila RNA-binding protein of the RNA recognition motif (RRM) class that functions during embryonic development and for the c ircadian regulation of adult eclosion. LARK protein contains three consensu s RNA-binding domains: two RRM domains and a retroviral-type zinc Finger (R TZF). To show that these three structural domains are required for function , we pet-formed a site-directed mutagenesis of the protein. The analysis of various mutations, in vivo, indicates that the RRM domains and the RTZF ar e required for LARK functions. RRM1 and RRM2 are essential for viability, a lthough interestingly either domain can suffice for this function. Remarkab ly, mutation of either RRM2 or the RTZF results in the same spectrum of phe notypes: mutants exhibit reduced,viability, abnormal wing and mechanosensor y bristle morphology, female sterility, and flightlessness. The severity of these phenotypes is similar in single mutants and double RRM2; RTZF mutant s, indicating a lack of additivity for the mutations and suggesting that RR M2 and the RTZF act together, in vivo, to determine LARK function. Finally, we show that mutations in RRM1, RRN12, or the RTZF do not affect the circa dian regulation of eclosion, and we discuss possible interpretations of the se results. This genetic analysis demonstrates that each of the LARK struct ural domains functions in vivo and indicates a pleiotropic requirement for both the LARK RRM2 and RTZF domains.