Pneumococci frequently colonize the upper respiratory tract, and these pneumococci are believed to act as a reservoir for infection of the lower respiratory tract and bacteremia. We investigated how the pneumococcal toxin pneumolysin affects the capacity of pneumococci to infect the upper and lower respiratory tract of the mouse. Wild-type Streptococcus pneumoniae serotype 2 and 3 strains, a serotype 2 pneumolysin-deficient mutant, and a serotype 2 mutant with the pneumolysin gene reinserted were used to study differences in colonization and disease. In addition, we also examined a pneumococcal chimeric mutant (capsule type switched from serotype 2 to serotype 3) to gain further insight into the role that capsule plays in nasopharyngeal infection. Absence of pneumolysin was found to be associated with significantly lower numbers of pneumococci in the nasopharynx, trachea, and lungs. Differences in pneumococcal capsule type were found to have significant effects on pneumococcal infection of the nasopharynx, trachea, and lungs. However, it was the combination of capsule type and genetic background that was important, and the influence of this combination varied with the site of infection. For example, in the nasopharynx the wild-type serotype 3 strain and the capsule-switched mutant behaved similarly, whereas in the lungs the mutant that was switched to serotype 3 survived less well than the wild-type serotype 3 strain. The combination of capsule type and genetic background also determined virulence. Thus, the wild-type serotype 3 strain was virulent, whereas the capsule-switched mutant was avirulent.Streptococcus pneumoniae (the pneumococcus) is a major cause of morbidity and mortality. It causes a wide variety of diseases ranging from pneumonia, meningitis, otitis media, septicemia, and sinusitis to comparatively benign soft tissue infections. The pneumococcus can also colonize the upper respiratory tract. It has been estimated that the upper respiratory tracts of 40% or more of children carry pneumococci. Furthermore, the pneumococcus is asymptomatically carried by healthy people in the upper respiratory tract, and depending on the age of onset, the environment of the host, and the presence of underlying respiratory infections, the carriage rate can vary from 5 to 70% (4,20,29).It is generally accepted that pneumococcal infection begins with the colonization of the nasopharynx, which allows progression of pneumococci into the lower parts of the respiratory tract, eventually leading to systemic disease (6, 23). Nasopharyngeal colonization also serves as an important reservoir of transmission to other susceptible individuals. The rapid increase in multiple-antibiotic-resistant strains and the high rate of pneumococcal carriage in children and the elderly, plus the problems that asymptomatic carriage presents for diagnosis, warrant further study of the virulence factors involved in nasopharyngeal colonization.The pneumococcal polysaccharide capsule and the multifunctional pneumococcal toxin pneumolysin are known t...

SummaryThe rRNA depurination activities of five ribosomeInactivating proteins (RIPs) were compared in vitro using yeast and tobacco leaf ribosomee as substrates. All of the RIPs (pokeweed antlvirel protein (PAP), dianthin 32, trltin, barley RIP end ricin A-chain) were active on yeast ribosomes. PAP and dlanthin 32 were highly active and ricin A-chain weekly active on tobacco ribosomes, whereas trltin and barley RIP were inactive. PAP and dlanthin 32 were highly effective in inhibiting the formation of local lesions caused by tobacco mosaic virus (TMV) on tobacco leaves, whereas tritin, barley RIP and ricin A-chain were ineffective. The apparent anomaly between the in vitro rRNA depurinatlon activity, but lack of antiviral activity of ricin A-chain was further Investigated by assaying for rRNA depurinstion in situ following the topical application of the RIP to leaves. No activity was detected, a finding consistent with the apparent lack of antlviral activity of this RIP. Thus, it is concluded that there is a positive correlation between RIP-catalyeed depurination of tobacco ribosomes and antlviral activity which gives strong support to the hypothesis that the antiviral activity of RIPs works through ribosome inactivation.

We have determined the complete nucleotide sequence of RNA1 of the tobravirus pea early browning virus [PEBV] from an overlapping series of cDNA clones. The 7073 nucleotide sequence contains four open reading frames [ORFs]. The 5' proximal ORF encodes a 141K polypeptide, and readthrough of the opal [UGA] termination codon of this ORF would lead to the synthesis of a second, 201K polypeptide. Both of these polypeptides have extensive amino acid homology with the putative replicase proteins of tobacco rattle virus [TRV] and tobacco mosaic virus [TMV]. The third ORF encodes a 30K polypeptide which has homology with the TRV 29K and TMV 30K putative cell-to-cell spread proteins. The fourth, 3' proximal ORF encodes a 12K polypeptide which has extensive homology with the TRV 16K protein whose function is unknown. Examination of the amino acid sequences of the 12K and 16K gene products reveals in each the presence of two multiple-cysteine/histidine motifs, a finding which suggests that these proteins might have zinc and/or nucleic acid-binding properties.

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