H. Benshlomo et al., THE TRYPANOSOMATID LEPTOMONAS-COLLOSOMA 7SL RNA GENE - ANALYSIS OF ELEMENTS CONTROLLING ITS EXPRESSION, Nucleic acids research, 25(24), 1997, pp. 4977-4984
We have previously reported the co-purification of a tRNA-like molecul
e with the Trypanosoma brucei SRP complex [Beja et al, (1993) Mel. Bio
chem, Parasitol, 57, 223-230]. To examine whether the trypanosome SRP
has a unique composition compared with that of other eukaryotes, we an
alyzed the 7SL RNA and the SRP complex of the monogenetic trypanosomat
id Leptomonas collosoma. The 7SL RNA from L.collosoma was cloned, and
its gene was sequenced, In contrast to T.brucei, two 7SL RNA transcrip
ts were detected in L.collosoma that originate from a single-copy gene
, Using stable cell lines expressing tagged 7SL RNA, we demonstrate th
at the tRNA(Arg) gene located 98 bp upstream to the 7SL RNA serves as
part of the 7SL RNA extragenic promoter, The steady-state level of 7SL
RNA was found to be tightly regulated, since the presence of the gene
on the multi-copy plasmid repressed the synthesis of the chromosomal
gene, Cell lines carrying truncated 7SL RNA genes were established and
their expression indicated that domain I is essential for expressing
the 7SL RNA, No constructs carrying portions of the 7SL RNA were expre
ssed, except for a construct which lacked 23 nt from the 3' end of the
RNA. This suggests that 90% of the 7SL RNA molecule is important for
its maintenance as a stable small RNA, We propose that the repression
phenomenon may originate from a regulatory mechanism that coordinates
the level of the 7SL RNA by its binding proteins.