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D. discoideurn has two alternative developmental pathways. If cells of two complement matingtype strains, NC4 and HM1, fuse sexually, a giant cell is produced which subsequently develops into a macrocyst, the sexual structure of this organism. However, if fusion fails to occur and cells are starved, a fruiting-body is produced instead of a macrocyst. In this paper, a two-dimensional polypeptide gel electrophoresis study showed that giant cells produce specific polypeptides which may possibly be involved in macrocyst development. Out of total 497 polypeptides which appeared in a giant cell during an incubation period of 13 hr, 92 were the specific for giant cells. Four of these polypeptides were appeared within only 1 hr after the cell fusion. The other 405 were non-specific polypeptides which appeared in both giant cells and NC4 oriand HM1 cells. However, the patterns and the rates of production of each polypeptide during the incubation period were different between these cells.

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We have investigated the in vivo function of a chimeric protein constructed by recombinant DNA techniques. The behavior and antitumor activity of a protein A‐lymphotoxin chimera (ALT) was examined on a murine tumor in mice in comparison with ammo‐terminal 19 amino acid‐deleted lymphotoxin (dLT), Seven‐week‐old male BALB/c mice were implanted intradermally with Meth‐A fibrosarcoma on day 0. ALT and dLT caused tumor regression, hemorrhagic necrosis and complete regression in a dose‐related way when each agent was given intratumorally 5 times (days 5–9). The ratio of the median effective doses for complete tumor regression was 1.6 between ALT and dLT on a molar basis. ALT caused tumor regression and body weight loss when given intravenously on the same schedule. Biodistribution studies with 125I‐labeled ALT and dLT demonstrated that, after intratumoral administration, ALT was retained longer in the administered site and was cleared more slowly from the mouse body than dLT. These findings suggest that a protein A‐lymphotoxin chimeric protein expresses both antitumor activity similar to that of lymphotoxin and characteristic in vivo behavior of the fused protein A portion.