Influenza remains a serious public health threat throughout the world. Vaccines and antivirals are available that can provide protection from infection. However, new viral strains emerge continuously because of the plasticity of the influenza genome, which necessitates annual reformulation of vaccine antigens, and resistance to antivirals can appear rapidly and become entrenched in circulating virus populations. In addition, the spread of new pandemic strains is difficult to contain because of the time required to engineer and manufacture effective vaccines. Monoclonal antibodies that target highly conserved viral epitopes might offer an alternative protection paradigm. Herein we describe the isolation of a panel of monoclonal antibodies derived from the IgG + memory B cells of healthy, human subjects that recognize a previously unknown conformational epitope within the ectodomain of the influenza matrix 2 protein, M2e. This antibody binding region is highly conserved in influenza A viruses, being present in nearly all strains detected to date, including highly pathogenic viruses that infect primarily birds and swine, and the current 2009 swine-origin H1N1 pandemic strain (S-OIV). Furthermore, these human anti-M2e monoclonal antibodies protect mice from lethal challenges with either H5N1 or H1N1 influenza viruses. These results suggest that viral M2e can elicit broadly cross-reactive and protective antibodies in humans. Accordingly, recombinant forms of these human antibodies may provide useful therapeutic agents to protect against infection from a broad spectrum of influenza A strains.

Telomerase is a ribonucleoprotein enzyme that adds telomeric sequence repeats to the ends of linear chromosomes. In vitro, telomerase has been observed to add repeats to a DNA oligonucleotide primer in a processive manner, leading to the postulation of a DNA anchor site separate from the catalytic site of the enzyme. We have substituted photoreactive 5-iododeoxypyrimidines into the DNA oligonucleotide primer d(T 4 G 4 T 4 G 4 T 4 G 2 ) and, upon irradiation, obtained cross-links with the anchor site of telomerase from Euplotes aediculatus nuclear extract. No cross-linking occurred with a primer having the same 5 end and a nontelomeric 3 end. These cross-links were shown to be between the DNA primer and (i) a protein moiety of approximately 130 kDa and (ii) U51-U52 of the telomerase RNA. The cross-linked primer could be extended by telomerase in the presence of [␣-32 P]dGTP, thus indicating that the 3 end was bound in the enzyme active site. The locations of the cross-links within the single-stranded primers were 20 to 22 nucleotides upstream of the 3 end, providing a measure of the length of DNA required to span the telomerase active and anchor sites. When the single-stranded primers are aligned with the G-rich strand of a Euplotes telomere, the cross-linked nucleotides correspond to the duplex region. Consistent with this finding, a cross-link to telomerase was obtained by substitution of 5-iododeoxycytidine into the CA strand of the duplex region of telomere analogs. We conclude that the anchor site in the ϳ130-kDa protein can bind duplex as well as single-stranded DNA, which may be critical for its function at chromosome ends. Quantitation of the processivity with single-stranded DNA primers and double-stranded primers with 3 tails showed that only 60% of the primer remains bound after each repeat addition.Telomeres are the terminal DNA-protein structures of eukaryotic chromosomes (for reviews see references 4 and 42). The DNA portion consists of simple sequence repeats, which in many organisms are rich in G and T nucleotides on the strand running 5Ј to 3Ј toward the end of the chromosome (3). In some ciliates, the GT strand has been shown to extend beyond the complementary CA strand, creating a singlestranded 3Ј end (21). Telomere proteins that recognize and bind to this DNA structure have been isolated and characterized from the hypotrichous ciliates Oxytricha nova (9,10,18,32) and Euplotes crassus (31, 33). The resulting DNA-protein telomere complex provides a protective cap on the end of the chromosome that is thought to prevent degradation and recombination of the chromosome ends.Telomeric DNA sequence repeats are synthesized de novo at the chromosome ends by a unique enzyme called telomerase (12). Telomerase is a ribonucleoprotein (RNP) containing a single RNA strand (13). The sequence of this RNA has been determined for several ciliate species, and a comparison of the sequences has revealed a conserved RNA secondary structure (26,28,34). These RNAs all contain a CA-rich region, complementary to the GT-...

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