Green fluorescence protein as a transcriptional reporter for the long terminal repeats of the human immunodeficiency virus type 1.

Using the enhanced green fluorescence protein (EGFP), a transient reporter expression system was established to assess the transcriptional activity of the long terminal repeats (LTR) of primary isolates of the human immunodeficiency virus type 1 (HIV-1). Consistent with the conventional chloramphenicol acetyl transferase (CAT) reporter, EGFP expression, under the direction of HIV-1 LTR, was readily detected in the transient transfection and was elevated by co-transfection of HIV-1 tat-expression vector. Comparing to CAT, however, EGFP expression system has two advantages: (i) Using a fluorescence activated cell sorter (FACS), it was possible to simultaneously measure transfection efficiency and fluorescence intensity of the transfected live cells without the necessity of co-transfection of a reference plasmid for comparing the transcriptional activity of two promoters; and (ii) EGFP expression was readily detected at a DNA concentration where CAT activity was not detectable possibly because the transfectants could be 'gated'. On the other hand, at a higher concentration of DNA, CAT signal became more prominent than that of EGFP, possibly because the enzymatic activity of CAT 'amplified' the signal. EGFP fluorescence detected by FACS was a direct measurement of the expressed chromophore. It is concluded that the system is rapid, reproducible, convenient and useful for quantitative analysis of transcription.