| Popis: |
A hallmark of CRISPR-Cas immunity systems is the CRISPR array, a genomic locus consisting of short, repeated sequences (“repeats”) interspersed with short, variable sequences (“spacers”). CRISPR arrays are transcribed and processed into individual CRISPR RNAs (crRNAs) that each include a single spacer, and direct Cas proteins to complementary sequence in invading nucleic acid. Most bacterial CRISPR array transcripts are unusually long for untranslated RNA, suggesting the existence of mechanisms to prevent premature transcription termination by Rho, a conserved bacterial transcription termination factor that rapidly terminates untranslated RNA. We show that CRISPR arrays of Salmonella Typhimurium are protected from Rho by the Nus factor anti-termination complex, and we provide evidence that this is an evolutionarily ancient mechanism to facilitate complete transcription of bacterial CRISPR arrays. |
