A third potential mechanism derives from the observation that the
translation termination codon of Tpase genes of certain elements is located
within their IR sequences. Although, to our knowledge, no extensive analysis of
the significance of this arrangement has yet been undertaken, it seems possible
that it may in some manner couple translation termination, transposase binding
and transposition activity. The transposase gene of several elements does not
possess a termination codon. These include IS240C, a member of the IS6 family (Y.Chen and J.Mahillon unpublished), two members of the IS5 family, IS427 (De Meirsman, et al., 1990) and ISMk1 (Mariani, et al.,
1993) and various members of the IS630 family including IS870 and ISRf1 (Fournier, et al.,
1993). Instead, some of these elements insert into a relatively specific target
sequence in which the target DR produced on insertion itself generates the
Tpase termination codon (see: IS630 family). The relevance of this as a control mechanism has yet to be explored.
Meirsman C, Van Soom C, Verreth C, Van Gool A & Vanderleyden J (1990)
Nucleotide sequence analysis of IS427 and its target sites in Agrobacterium
tumefaciens T37. Plasmid 24: 227-234.
P, Paulus F & Otten L (1993) IS870 requires a 5'-CTAG-3' target sequence to
generate the stop codon for its large ORF1. J
Bacteriol. 175: 3151-3160.
- Mariani F, Piccolella E, Colizzi V,
Rappuoli R & Gross R (1993) Characterization of an IS-like element from
Mycobacterium tuberculosis. J
Gen.Microbiol. 139: 1767-1772.