A synthetic nucleic acid molecule is provided that includes nucleotides of a coding region for a fluorescent polypeptide having a codon composition differing at more than 25% of the codons from a parent nucleic acid sequence encoding a fluorescent polypeptide. The synthetic nucleic acid molecule has at least 3-fold fewer transcription regulatory sequences relative to the average number of such sequences in the parent nucleic acid sequence. The polypeptide encoded by the synthetic nucleic acid molecule preferably has at least 85% sequence identity to the polypeptide encoded by the parent nucleic acid sequence.