Thermus phage Lalka27a
- Morphotype
- myovirus
- Lifecycle
- lysogenic
- Genome type
- dsDNA
- Genome length, bp
- 71 251
- GC content, %
- 70.6
- Isolation source
- Valentina hot springs, Kunashir Island
- Accession
- PQ109076
Genome map
Sequences
| File | Kind | Version | Size |
|---|---|---|---|
| Lalka27a_genome.gb.gz | annotation | 48 KB |
Description
Lalka27a, along with the related Lalka phages, encodes its own Type V CRISPR-Cas system, consisting of a Cas12r1 protein and a CRISPR array. It is worth to mention that the Lalka phages are among the few cultivated phage isolates known to harboring a CRISPR-Cas system (the only other examples are the Vibrio cholerae phages ICP1; all other cases reported to date are viral sequences recovered from metagenomes). The functions of the Lalka-encoded CRISPR-Cas system is still unclear; look at this note for the details.
With the exception of Lalka27b, which lacks an integrase gene, all Lalka phages appear to be capable of integrating into the host genome at the 3'-proximal segment of an alanine tRNA gene. In this aspect Lalka phages resemble other lysogenic Thermus phages, like phiMa, Cumys, Riverbug and Tsatsa.
Lalka27a infects T. thermophilus HB27c, yielding titers of up to 10¹⁰ PFU/ml upon lysis of a liquid culture. The closely related strain T. thermophilus HB27, however, appears to be partially resistant: it gives a reduced efficiency of plating and smaller plaques.
Lalka phages encode several virionic proteins which apparently are injected into the host cell upon the infection:
- Ulx (Lalka27a_1) - a homolog of phage P1 Ulx protein, which is required for protection against host type I restriction-modification (R-M) systems
- DarB (Lalka27a_2) - a homolog of P1 DarB, which is likewise required for protection against host type I R-M systems. The presence of DarB in Lalka27a virions was confirmed by proteomic analysis;
- Gp4 (Lalka27a_4) - detected in virions by proteomic analysis, but its functions are obscure. Given its proximity to the darB-ulx operon it might be possible that Gp4 is also involved in the protection against host type I RM systems;
- Lvh (large virion helicase Lalka27a_41) - a large protein with a predicted helicase domain. Homologs of Lalka Lvh are encoded by phiMa/Cumys phages, distant relatives of Lalka phages.