Lentiviral short hairpin RNA (shRNA) knockdown vectors have emerged as the industry standard for both transient and stable knockdown of individual genes. The lentivirus is easy to make using Invitrogen's ViraPower kit, which is recommended. Efficiency of infection approaches 100 percent in a wide variety of cell lines, including postmitotic cells and primary cell cultures. Efficiency of knockdown in the range of 70 to 95 percent is routinely achieved.

The RNA Interference Shared Resource at Mayo Clinic offers the complete Sigma-Aldrich Mission RNA interference (RNAi) line of lentiviral vectors, with a large in-house library that continues to grow. The experiences of lab members indicate that the Sigma-Aldrich RNAi vectors are reliable, relatively trouble-free and the optimum "workhorse" platform for initial characterization of RNAi knockdown effects.

A number of companies offer lentiviral and other shRNA expression vectors, and some of these vectors appear to have features that make them attractive for specialized purposes. The RNA Interference Shared Resource offers one of these libraries, the GIPZ library from Open Biosystems. This library is made up of shRNA sequences in a larger backbone engineered to express green fluorescent protein as an easily detected positive control. Investigators logged onto the Mayo Clinic network can access the internal RNA Interference Shared Resource site on Mayo's intranet Web portal. (Requires login to the Mayo Clinic network).