SAMHD1 and HIV-1 infection: However, in addition the non-phosphorylatable mutants in the Tetstable group together with T592A, that could all restrict HIV-1 infection in differentiated cells, were also not able to restrict HIV-1 in these cycling cells (Fig. 3B) suggesting that prevention of SAMHD1 phosphorylation and maintenance of a stable tetramer is not enough to restrict HIV-1 replication in cycling cells.