With ~1/3 of Streptomyces genomes carrying telomeric transposons, these elements compete for the same niche. Identical transposons in different telomeres, both within and between genomes, are occasionally found to be disrupted by other transposons, indicating fierce competition.

TnsBC telomeric transposons are highly diverse, with distinct gene repertoires. Surprisingly, one subgroup includes the Type I-E Cascade + tnsBC system. The tnsBC was initially thought to replace Cas1-Cas2. Spacer analysis supports their telomeric role, often targeting ttrA.

Tn7-like telomeric transposons encode TnsA, which mediates cointegrate resolution. We hypothesized that TnsA is inactive, as cut-and-paste transposition would harm one-ended transposons. Active site analysis confirmed that conserved residues in non-telomeric transposons are altered.

Following PASTs, we searched telomeric transposons by clustering and mapping the locations and orientations of DDE family transposases in Streptomyces. This analysis identified two groups of telomeric transposons: Tn7-like and the other containing only conserved tnsB and tnsC.

Initially mistaken as "broken" V-K CASTs near contig ends, PASTs are linked to a small protein gene and a downstream protelomerase (TelT). We confirmed these contig ends as true termini maintained by TelT. The transposon preferentially targets linearized E. coli chromosome ends.

These elements, with a single transposon end and a telomere-defined opposite end, act as mobile telomeres. Their lifestyle ensures host dependence and may facilitate conjugative transfer via TtrA-mediated telomere mobilization in Streptomyces, contributing to telomere turnover.

Initially mistaken as "broken" V-K CASTs near contig ends, PASTs are linked to a small protein gene and a downstream protelomerase (TelT). We confirmed these contig ends as true termini maintained by TelT. The transposon preferentially targets linearized E. coli chromosome ends.

These elements, with a single transposon end and a telomere-defined opposite end, act as mobile telomeres. Their lifestyle ensures host dependence and may facilitate conjugative transfer via TtrA-mediated telomere mobilization in Streptomyces, contributing to telomere turnover.