UASp regulatory sequences drive expression of a mutant form of SmB in which the four distal Arg residues (residues 174, 181, 189 and 196) out of the seven Arg residues in SmB which are present in RG dipeptide repeats and can potentially be methylated have been substituted (either by Leu or Gly).
Expression of SmBR4-7.Scer\UAS.P\T under the control of Scer\GAL4tub.PU rescues the lethality of SmBBG02775/SmBSH0509 with an efficiency of 37%. Rescued females have smaller ovaries than normal and contain mostly previtellogenic egg chambers. Most egg chambers that have reached the end of previtellogenic development show signs of degeneration, including a condensed nuclear morphology. A small fraction of egg chambers complete development. Embryos derived from the few eggs laid by the rescued females build a normal layer of blastoderm cells, but fail to form pole cells.