[
Worm Breeder's Gazette,
1990]
A subset of C. elegans mRNAs receives a 22 nucleotide leader from a precursor RNA called SL RNA. This RNA has the hallmarks of a typical snRNA: it is bound to the 'Sm' proteins and it has the unusual cap nucleoside, trimethylguanosine (TMG). Because this cap is on the 5' end of SL RNA it is transferred to recipient RNAs, along with the 22 nucleotides, during trans-splicing. Originally we believed this unusual cap was subsequently altered or removed, but it isn't. Since translation in eukaryotes is initiated by binding of an initiation factor, eIF-4E, to the cap (normally monomethylguanosine) the presence of a different cap on some mRNAs could have important functional consequences. For this reason (and also because a reviewer suggested it might be a good idea) we undertook to find out whether these TMG-capped mRNAs are found on polysomes. We made polysomes from young adult worms by a procedure adapted from a method for making plant polysomes. The procedure is briefly outlined below. We then used anti-TMG antibodies to demonstrate that actin-1 and actin-3 mRNAs found in the polysome preparation are indeed TMG capped. We conclude that TMG-capped mRNAs are translated in C. elegans. Several mechanisms by which translation may be initiated on these mRNAs are possible: 1. C. elegans eIF-4E might recognize both kinds of cap structure.