Fig. 1. Constructs for the potential triggering of cop-silencing in Chlamydomonas. The efficiency of different silencing constructs was determined by measuring the decreased opsin levels in transformants obtained with each plasmid. Construct pMF15 was designed to induce cosuppression by providing a cop gene containing a nonsense mutation early in the gene (*). The constructs pMF38-47 provided a single ‘antisense RNA’ to target cop-mRNA under the control of a strong promotor. Arrows show the antisense portions of the cop-gene. Numbers within black segments of the diagram correspond to the position of exons in the cop-gene.%PTGS is calculated as the number of clones showing a reduction in chlamyopsin of more than 20% divided by the number of tested clones (n). %r is the amount of residual Cop protein in the mutant with the lowest observed Cop-level in each experiment.