A method of determining whether a molecule not previously known to be a modulator of protein biosynthesis is capable of transcriptionally modulating the expression of a gene-of-interest which comprises contacting a sample which contains a predefined number of cells with a predetermined amount of a molecule to be tested, each such cell comprising DNA consisting essentially of (i) a modulatable transcriptional regulatory sequence of the gene-of-interest, (ii) a promoter of the gene-of-interest, and (iii) a reporter gene, which expresses a polypeptide capable of producing a detectable signal, coupled to, and under the control of, the promoter, under conditions such that the molecule, if capable of acting as a transcriptional modulator of the gene-of-interest, causes a measureable detectable signal to be produced by the polypeptide expressed by the reporter gene, quantitatively determining the amount of the signal produced, comparing the amount so determined with the amount of produced signal detected in the absence of any molecule being tested or upon contacting the sample with any other molecule, and thereby identifying the molecule as one which causes a change in the detectable signal produced by the polypeptide expressed by the reporter gene, and thus identifying the molecule as a molecule capable of transcriptionally modulating the expression of the gene-of-interest.