We have isolated three cDNA clones for p2-microglobulin, the small subunit of the major histocompatibility antigens. .82-Microglobulin makes up less than 0.1% of mouse liver protein, and its mRNA is approximately 0.03% of liver poly(A)+ mRNA. The cDNA clones were identified by screening 1400 cDNA clones made from 9-1OS mouse liver poly(A)+ mRNA. The procedure for screening the cDNA clones involved binding pooled plasmid DNA to nitrocellulose filters and testing the ability ofeach filter to select .32-microglobulin mRNA. The filter-selected mRNAs were assayed for their ability to direct the synthesis of P2-microglobulin in translation reactions in vitro. The isolated clones were shown by nucleotide sequence analysis to encode (32-microglobulin. The positive-selection-hybridization assay has been modified to facilitate the screening of large numbers of cDNA clones, and the modified assay should allow the isolation ofcDNAs corresponding to any mRNA whose in vitro translation products can be immunoprecipitated. These modifications are of particular value in the isolation ofcDNA clones corresponding to rare species of mRNA.

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The relationship between cell pigmentation and radiosensitivity was investigated in a cell model in which melanogenesis was suppressed by a glycosylation inhibitor. It was found that X-irradiation of melanotic B-16 melanoma cells and their amelanotic counterparts, obtained by glucosamine treatment, showed an inverse correlation between radiosensitivity and melanin contents. Since melanogenesis interruption by glucosamine does not affect the DNA repair capacity of nonpigmented cells, it is likely that intracellular melanins play a role in the relative resistance of pigmented cells to X-irradiation.

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The serum levels of immunosuppressive acid protein (IAP) and CA 125 were determined in 98 patients with ovarian cancer, in 20 patients with benign ovarian tumors and in a group of normal postmenopausal women as controls. On the basis of the mean values of normal controls (346.46 ± 133.26 μg/ml), the IAP threshold was fixed at 613 ∣ig/ml. Increased IAP levels were found in 70.4% of patients with ovarian cancer, in 25% of benign tumors and in 4.5% of normal women. Elevated levels of CA 125 were observed in 66.6% of cancers, in 40% of benign tumors and in 6.9% of controls. In particular, in early stage ovarian cancer the combined assay of the two markers increased by about 30% with respect to CA 125 alone. The simultaneous determination of IAP and CA 125 allowed an overall sensitivity of 84% without any significant reduction of specificity.