Final answer:
The main point of control for regulating gene expression levels is transcription. This is where the DNA information is transcribed to mRNA and is highly regulated by various transcription factors and mechanisms. While other controls exist post-transcription, transcription is the most influential.
Step-by-step explanation:
The main point of control for regulating gene expression levels is transcription. During transcription, the information in a gene's DNA is transferred to mRNA, which then serves as a template for protein synthesis during translation. Regulation can occur here through mechanisms such as the binding of transcription factors to DNA, the modification of histones affecting DNA accessibility, and the initiation of transcription itself. Eukaryotic cells, in particular, have complex transcriptional regulation involving additional elements such as enhancers and silencers, which can dramatically influence gene expression.
Other points of control in gene expression include mRNA degradation and protein degradation, but these are generally considered secondary to transcription in terms of influence. Post-transcriptional events, such as RNA splicing, do play a significant role, but primarily after the transcriptional control has taken place. Translation can also be regulated, for example, by controlling the binding of mRNA to the ribosome or through translational repressors that prevent the synthesis of proteins at the ribosome level, but again these are dependent on transcription having already occurred.
Thus, while other stages of gene expression have their roles, transcription remains the primary and most influential point of regulating gene expression levels.