Synthetic nucleic acid molecule compositions and methods of preparation

An isolated nucleic acid molecule comprising a synthetic nucleotide sequence encoding a firefly luciferase comprising a fragment of at least 300 nucleotides having 80% or less nucleic acid sequence identity to a parent nucleic acid sequence having SEQ ID NO:43 or 85% or less nucleic acid sequence identity to a parent nucleic acid sequence having SEQ ID NO:14 and having 99% or more nucleic acid sequence identity to SEQ ID NO:21, SEQ ID NO:22 or SEQ ID NO:23 or the complement thereof, wherein the decreased sequence identity is a result of different codons in the synthetic nucleotide sequence relative to the codons in the parent nucleic acid sequence, wherein the synthetic nucleotide sequence encodes a firefly luciferase which has at least 85% amino acid sequence identity to the corresponding luciferase encoded by the parent nucleic acid sequence, and wherein the synthetic nucleotide sequence has a reduced number of regulatory sequences relative to the parent nucleic acid sequence.