RNA Helicase 1 interacts with an ABCRNAi Transporter: Genetic Interactions with haf-6

Abstract

The C. elegans rha-1 gene encodes a conserved helicase with ATP-dependent DEAD/H-box and double-stranded RNA binding domains. rha-1 is orthologous to the Drosophila maleless gene(MLE), an essential component of the dosage compensation machinery that leads to a two-fold increase in transcription of genes located on the single X chromosome of males in comparison to the transcription rate of homologous genes located on an X chromosome in females. The human ortholog, RNA helicase A (RHA), unwinds double-stranded DNA and RNA in a 3' to 5' direction. RHA is a component of several distinct protein complexes, including the RNA-induced silencing complex (RISC), the coding region determinant (CRD)-mediated complex, mRNP granules, and also associates with BRCA1, CREBbp or SMN1 and the RNA polymerase II complex, phosphorylated histones (H2AFX). RHA affects a number of different biological activities, including CRD-mediated mRNA stabilization, RNA splicing, translation, and transcription. It also has been discovered that regulation of RHA is disrupted in many types of cancers. The C. elegans rha-1 gene is expressed in the gonad where it localizes to the nucleus and the cytoplasm and is required for proper development. Defects in rha-1 lead to germline defects, aberrant expression of genes residing in repetitive transgene arrays, and defects in RNAi. ABC transporter proteins have also been implicated to play a role in RNAi in C. elegans. Ten out of the sixty-one ABC transporters are required for efficient RNAi in the germ line; these transporters are called ABCRNAi transporters. All of the ABCRNAi transporter mutants interact genetically with rde-2 (a novel protein) and mut-7 (a protein with homology to RnaseD). One of these ABCRNAi transporter genes is haf-6. The works presented here show that rha-1 mutants also interact genetically with haf-6, with rde-2, and with mut-7 with respect to RNAi defects. By contrast, mutations in rha-1 suppress the transposon mobilization phenotypes observed in haf-6 mutants. It is also observed that an unknown mutation is genetically interacting with rha-1 and haf-6. We are currently investigating roles for rha-1 in proper accumulation of haf-6 and other ABCRNAi transporter mRNAs in an effort to understand the interrelated functions of these proteins in RNAi.