Affiliations: Department of Biochemistry and Molecular Biology,
University of Dhaka, Bangladesh | Department of Family Sciences, College for Women,
Kuwait University, Kuwait | Department of Pathology, Case Western Reserve
University, Cleveland, OH, USA
Note: [] Corresponding author: Mohammad Arif, Department of Biochemistry
and Molecular Biology, University of Dhaka, Dhaka-1000, Bangladesh. Tel.: +880
2 9661900 59, Ext: 7643; Fax: +880 2 8615583; E-mail: marif567@yahoo.com,
marif@univdhaka.edu
Abstract: Bacteria have developed several defense mechanisms against
bacteriophages over evolutionary time, but the concept of prokaryotic RNA
interference mediated defense mechanism against phages and other invading
genetic elements has emerged only recently. Clustered regularly interspaced
short palindromic repeats (CRISPR) together with closely associated genes (cas genes)
constitute the CASS system that is believed to provide a RNAi-like
defense mechanism against bacteriophages within the host bacterium. However, a
CASS mediated RNAi-like pathway in enteric pathogens such as Vibrio
cholerae O395 or Escherichia coli O157 have not been reported yet. This
study specifically was designed to investigate the possibility and evolutionary
origin of CASS mediated RNAi-like pathway in the genome of a set of enteric
pathogens, especially V. cholerae. The results showed that V.
cholerae O395 and also other related enteric pathogens have the essential CASS
components (CRISPR and cas genes) to mediate a RNAi-like pathway. The
functional domains of a V. cholerae Cas3 protein, which is believed to
act as a prokaryotic Dicer, was revealed and compared with the domains of
eukaryotic Dicer proteins. Extensive homology in several functional domains
provides significant evidence that the Cas3 protein has the essential domains
to play a vital role in RNAi like pathway in V. cholerae. The secondary
structure of the pre-siRNA for V. cholerae O395 was determined and its
thermodynamic stability also reinforced the previous findings and signifies the
probability of a RNAi-like pathway in V. cholerae O395.
Keywords: CRISPR, cas genes, prokaryotic RNA interference, Vibrio cholerae O395
