The signal sequence of the p62 protein of Semliki Forest virus is involved in initiation but not in completing chain translocation

In lanes 10--16 we have analyzed the samples that were withdrawn at the different times but were kept on ice. As expected, we see a sequential appearance of first the capsid The Journal of Cell Biology, Volume 111, 1990 protein (in the 10-min sample) and then the p62 d-4 protein (barely visible in the 20-min sample). The p62 d-4 protein is partly present in its glycosylated and partly in its unglycosylated form. Using 21.5 min as a rough estimate for the translation time of the 746 residue long C-p62 d-4 chain (time point of p62 d-4 detection, 20 min, plus half of the 3-min preincubation time without ATA) we have calculated the translation rate and derived the approximate earliest time points when the four glycosylation sites of p62 d-4 should be available for modification. According to these, Asn~ and Asn60 should be the only sites available for glycosylation in the 10-min sample, shown in lane 4, and the most abundant ones presented for modification in the 15-min sample, shown in lane 5. Therefore, it appears reasonable to assume that those chains of these two samples which have obtained two sugar units carry these on the aforementioned two sites. Thus, the peptide region with Asn,a seems to be target for rapid modification also when present in its normal background, that is with the p62 protein.