Cell Microinjection: In Vivo Analysis of the Functional Domains of Viral Regulatory Proteins

Mammalian-cell microinjection is a powerful method for analyzing the in vivo functions of viral genes and viral gene products. By microinjection, a controlled amount (ranging from 1 to many thousands of copies) of a viral or cellular gene, a protein product of a gene, a polypeptide fragment encoding a specific protein domain, or an RNA molecule can be delivered into a target cell and the functional consequences analyzed. Injection of DNA into the nuclei of cultured mammalian cells provides a sensitive bioassay for gene expression. The product of a single injected gene copy can be detected using standard immunofluorescent, immunochemical, and autoradiographic techniques (1 ). The direct analysis of protein function by microinjection has been facilitated by the ability to produce biologically active recombinant proteins and protein fragments encoded by many interesting genes.