The existence of a posttranslational pathway for ER targeting in mammalian cells was not known at the beginning of my thesis. In the first part of my thesis it was shown that, mammalian cells possess an alternative posttranslational protein-targeting pathway for small-secreted proteins and are dependent on the ER membrane protein Sec62. In the second part of the thesis we showed that an excess of SR and SRP68 subunit in the cell could lead to increase in secretion of the reporters. This increase was not depended on the ability of the SRP68 to assemble into the SRP complex, since a mutant also lead to an increase in secretion of the reporter proteins. Even though the mechanistic aspects of our observations are not clear, SRP68 might have additional functions outside the SRP complex, presumably at the translocational levels to regulate the secretory capacity of the cells.