CorrectionsMICROBIOLOGY. For the article ''Kaposi's sarcoma-associated herpesvirus encodes two proteins that block cell surface display of MHC class I chains by enhancing their endocytosis'' by Laurent Coscoy and Don Ganem, which appeared in number 14, July 5, 2000, of Proc. Natl. Acad. Sci. USA (97, 8051-8056; First Published June 20, 2000; 10.1073͞pnas.140129797), the authors note that in Fig. 3A, images of the identical gel were inadvertently reproduced twice, once in the control row and once in the experimental row. The error occurred during figure preparation and reflects the fact that in both the control and the experimental cell lines, MHC-I chains are processed identically, generating images that are very similar. The corrected Fig. 3A and its legend are printed below. No conclusions of the paper are affected.MEDICAL SCIENCES. For the article ''Human lung cancer and p53: The interplay between mutagenesis and selection'' by Sergei N. Rodin and Andrew S. Rodin, which appeared in number 22, October 24, 2000, of Proc. Natl. Acad. Sci. USA (97, 12244-12249; First Published October 17, 2000; 10.1073͞pnas.180320897), the authors note the following correction. Fig. 2 shows erroneous spectra that do not correspond to the test result (0.979 P value as described in the text) because the lung cancer spectrum in smokers was constructed when erroneous repeats were not removed from the IARC p53 mutational database (April 1999). Also, some mutations were assigned to the wrong cancer type classes because of a spreadsheet macro programming error during the building of the chart. Fig. 2 is repeated here with the correct spectra. These corrections do not change the results or the conclusions reported in the paper. were metabolically labeled for 20 min and chased for the indicated time periods. After being lysed in 1% Nonidet P-40, lysates were divided into three aliquots. Two were kept on ice and one was incubated at 37°C for 1 h. Heterodimeric MHC I molecules were immunoprecipitated with mAb W6͞32 and treated with endo H where indicated. Fig. 2.Comparison of the p53 spectra of G3 T transversions from lung cancer (cases related to radon and other occupational exposures excluded) of ever smokers and cancers in non-lung tissues least accessible to smoke (see Table 1). The size of the bars represents the G3 T frequency at the corresponding guanine. Hot-and ''warm''-spot codons are indicated. A major arm of host immunity to viral infection is the cytotoxic T lymphocyte (CTL), which recognizes viral antigens presented as peptides bound to class I MHC (MHC I) molecules on the surface of infected cells. CTL recognition of such cells can lead to direct cytolysis as well as the release of cytokines that can contribute further to antiviral action and host immune mobilization. Therefore, evasion of CTL recognition is thought to play a key role in the establishment of a systemic viral infection. Consistent with this view, many viruses have evolved complex strategies for such evasion, usually centering on the down-regulation of cell ...

Ubiquitination controls a broad range of cellular functions. The last step of the ubiquitination pathway is regulated by enzyme type 3 (E3) ubiquitin ligases. E3 enzymes are responsible for substrate specificity and catalyze the formation of an isopeptide bond between a lysine residue of the substrate (or the N terminus of the substrate) and ubiquitin. MIR1 and MIR2 are two E3 ubiquitin ligases encoded by Kaposi's sarcoma–associated herpesvirus that mediate the ubiquitination of major histocompatibility complex class I (MHC I) molecules and subsequent internalization. Here, we found that MIR1, but not MIR2, promoted down-regulation of MHC I molecules lacking lysine residues in their intracytoplasmic domain. In the presence of MIR1, these MHC I molecules were ubiquitinated, and their association with ubiquitin was sensitive to β 2 -mercaptoethanol, unlike lysine-ubiquitin bonds. This form of ubiquitination required a cysteine residue in the intracytoplasmic tail of MHC I molecules. An MHC I molecule containing a single cysteine residue in an artificial glycine and alanine intracytoplasmic domain was endocytosed and degraded in the presence of MIR1. Thus, ubiquitination can occur on proteins lacking accessible lysines or an accessible N terminus.

Kaposi's sarcoma-associated herpesvirus encodes two transmembrane proteins (modulator of immune recognition [MIR]1 and MIR2) that downregulate cell surface molecules (MHC-I, B7.2, and ICAM-1) involved in the immune recognition of infected cells. This downregulation results from enhanced endocytosis and subsequent endolysosomal degradation of the target proteins. Here, we show that expression of MIR1 and MIR2 leads to ubiquitination of the cytosolic tail of their target proteins and that ubiquitination is essential for their removal from the cell surface. MIR1 and MIR2 both contain cytosolic zinc fingers of the PHD subfamily, and these structures are required for this activity. In vitro, addition of a MIR2–glutathione S-transferase (GST) fusion protein to purified E1 and E2 enzymes leads to transfer of ubiquitin (Ub) to GST-containing targets in an ATP- and E2-dependent fashion; this reaction is abolished by mutation of the Zn-coordinating residues of the PHD domain. Thus, MIR2 defines a novel class of membrane-bound E3 Ub ligases that modulates the trafficking of host cell membrane proteins.

The detection of viral pathogens is of critical importance in biology, medicine, and agriculture. Unfortunately, existing techniques to screen for a broad spectrum of viruses suffer from severe limitations. To facilitate the comprehensive and unbiased analysis of viral prevalence in a given biological setting, we have developed a genomic strategy for highly parallel viral screening. The cornerstone of this approach is a long oligonucleotide (70-mer) DNA microarray capable of simultaneously detecting hundreds of viruses. Using virally infected cell cultures, we were able to efficiently detect and identify many diverse viruses. Related viral serotypes could be distinguished by the unique pattern of hybridization generated by each virus. Furthermore, by selecting microarray elements derived from highly conserved regions within viral families, individual viruses that were not explicitly represented on the microarray were still detected, raising the possibility that this approach could be used for virus discovery. Finally, by using a random PCR amplification strategy in conjunction with the microarray, we were able to detect multiple viruses in human respiratory specimens without the use of sequence-specific or degenerate primers. This method is versatile and greatly expands the spectrum of detectable viruses in a single assay while simultaneously providing the capability to discriminate among viral subtypes.