Strict conservation of the ITS regions of the ribosomal RNA genes in Atlantic cod (Gadus morhua L.).

The nucleotide sequence of the internal transcribed region (ITS) of ribosomal RNA genes from Atlantic cod (Gadus morhua L.) was determined. The complete ITS region spanned approximately 1113 base pairs. The ITS1 region comprised 532 base pairs, the 5.8S region 159, and the ITS2 region contained 422 base pairs. Sequence data were obtained from a total of 12 samples, one pool from six cod and 11 individuals. The sequencing was carried out in two separate experimental periods employing slightly different methodology. The samples were from two different cod stocks, Norwegian costal cod and North East Arctic cod. The sequence analysis showed that in the 12 samples, the ITS region, including the 5.8S RNA, was identical. The ITS region is thus totally conserved in these two cod stocks. The extreme conservation of the ITS regions in the cod rDNA could reflect the small genome size of cod and/or indicate a specific critical role in the processing of the ribosomal units in cold-adapted species.

Infectious salmon anemia virus specifically binds to and hydrolyzes 4-O-acetylated sialic acids.

Infectious salmon anemia virus (ISAV) is the causative agent of infections in farmed Atlantic salmon. ISAV presumably represents a new genus within the Orthomyxoviridae. ISAV has been shown earlier to exhibit a receptor-destroying activity, which was defined as an acetylesterase with unknown specificity. We have analyzed the substrate specificity of the ISAV esterase in detail. Purified ISAV hydrolyzed free 5-N-acetyl-4-O-acetyl neuraminic acid. In addition, the purified 9-O-acetylated sialic acid derivative was also hydrolyzed, but at lower rates. When we used a glycosidically bound substrate, ISAV was unable to hydrolyze 9-O-acetylated sialic acid, which represents the major substrate for the influenza C virus esterase. ISAV completely de-O-acetylated glycoprotein-bound 5-N-acetyl-4-O-acetyl neuraminic acid. Thus, the enzymatic activity of the hemagglutinin-esterase of ISAV is comparable to that of the sialate-4-O-esterases of murine coronaviruses and related group 2 coronaviruses. In addition, we found that ISAV specifically binds to glycoproteins containing 4-O-acetylated sialic acids. Both the ISAV esterase and recombinant rat coronavirus esterase specific for 4-O-acetylated sialic acids hydrolyzed ISAV receptors on horse and rabbit erythrocytes, indicating that this sialic acid represents a receptor determinant for ISAV.