Translation of an mRNA can be impeded by both micoRNAs and double-stranded RNAs in prokaryotes. ...

Expression of a microRNA results in the destruction of all mRNA complementary to it. MicroRNA is complementary to a part of mRNA and it base-pairs with the mRNA to form a double-stranded region. This double-stranded RNA is digested by enzyme complexes which destroys the mRNA. Without the mRNA, translation cannot occur.

In the case of double-stranded RNAs, such as in bacteria, an antisense RNA (one that is complementary in sequence to the mRNA), base-pairs with the mRNA. Once the mRNA is bound up by the antisense RNA, ribosomes cannot initiate translation.

Therefore, microRNA leads to mRNA destruction and double-stranded RNA prevents access to ribosomes. Both of these processes prevent translation.