Final answer:
The two protein types that regulate gene transcription are transcription factors, which can either promote or inhibit gene expression, and regulatory proteins like activators and repressors, which respectively increase or decrease transcription.
Step-by-step explanation:
The two types of proteins that influence the transcriptional expression of genes, effectively turning them on or off, are known as transcription factors and regulatory proteins such as repressors and activators. Transcription factors are a class of proteins that bind to specific genes on the DNA molecule to promote or inhibit their transcription, thus playing a key role in cell differentiation and function. In prokaryotic cells, regulation also involves proteins like activators, which increase transcription, and repressors, which suppress it, as well as inducers, which can bind to repressors and influence their activity.
In eukaryotic cells, gene expression can be precisely controlled by proteins binding to DNA regulatory elements, such as enhancers or silencers, sometimes located far from the gene itself. These regulatory elements and the proteins that bind to them are essential in the development of organisms and play roles in diseases such as cancer when mutated.