Many efforts for identify and detect small SwaI fragments tagging with the transposable elements were done without result, to solve this problem, partial digestions in wild type Psm chromosome were assayed.
The rare cutting restriction endonucleases PacI, PmeI, and SwaI were previously reported for construction physical maps in bacteria (21,22,25,26).
Artificial transposable elements pTn5cat1 and pTn5Spcat endowed with restriction sites for PacI, PmeI and SwaI (unpublished) were used to obtain a collection of insertional mutants, each with an extra restriction site for these endonucleases.
Although the correct position of the smallest SwaI fragments was not detected by partial digestions, further analysis with insertional mutants of Psm could determinate the order in the physical map.
maculicola M2 chromosome digested with PacI, PmeI and SwaI, with 14, 15 and 16 fragments, respectively.
Large-sized fragments by PFGE from Psm DNA chromosome digested with SwaI. (WT) Psm wild type strain, (16, 21) Psm pTn5cat mutants.
PFGE analysis of Psm insertional mutants digested with PacI, PmeI and SwaI. (6i, 7i) Psm pTn5cat1 mutants, (6, 18) Psm pTn5cat mutants and (WT) Psm wild type strain.