Northern blot analysis is performed on cellular mRNA isolated from E. coli. The probe used in the northern blot analysis hybridizes to a portion of the lacY sequence. Below is an example of the gel from northern blot analysis for a wild-type lac⁺ bacterial strain. In this gel, lane 1 is from bacteria grown in a medium containing only glucose (minimal medium). Lane 2 is from bacteria in a medium containing only lactose. Following the style of this diagram, draw the gel appearance for northern blots of the bacteria listed below. In each case, lane 1 is for mRNA isolated after growth in a glucose-containing (minimal) medium, and lane 2 is for mRNA isolated after growth in a lactose-only medium.

lac⁻ bacteria with the genotype I⁺ P⁻ O^C Z⁺ Y⁺

Verified step by step guidance

1. Understand the context of the problem: Northern blot analysis is used to detect specific RNA sequences. In this case, the probe hybridizes to the lacY mRNA, which encodes the lactose permease enzyme. The appearance of bands on the gel indicates the presence of lacY mRNA under specific growth conditions.
2. Analyze the genotype provided: The genotype is I⁺ P⁻ Oᶜ Z⁺ Y⁺. Here, I⁺ indicates a functional lacI repressor, P⁻ indicates a non-functional promoter, Oᶜ indicates a constitutive operator mutation, Z⁺ indicates a functional lacZ gene, and Y⁺ indicates a functional lacY gene.
3. Determine the effect of the P⁻ mutation: A non-functional promoter (P⁻) means that transcription of the lac operon cannot occur from this promoter, regardless of the presence of lactose or glucose. However, the Oᶜ mutation allows constitutive expression of the operon, bypassing the repressor's control.
4. Predict the expression of lacY mRNA: Since the Oᶜ mutation allows constitutive expression, lacY mRNA will be transcribed continuously, but only if the transcription machinery can access the operon. The P⁻ mutation prevents transcription from occurring, so no lacY mRNA will be produced in either glucose or lactose conditions.
5. Draw the gel appearance: For both lane 1 (glucose medium) and lane 2 (lactose medium), there will be no bands visible on the gel because no lacY mRNA is produced due to the P⁻ mutation.

Key Concepts

Northern Blotting

Northern blotting is a technique used to detect specific RNA sequences in a sample. It involves the separation of RNA by gel electrophoresis, transfer to a membrane, and hybridization with a labeled probe that binds to the target RNA. This method allows researchers to analyze gene expression by comparing the levels of mRNA in different conditions or treatments.

Lac Operon

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of structural genes (lacZ, lacY, and lacA) and regulatory elements that control their expression. The operon is typically activated in the presence of lactose and repressed when glucose is available, illustrating the concept of catabolite repression in bacterial gene regulation.

Genotype and Phenotype

Genotype refers to the genetic constitution of an organism, while phenotype is the observable characteristics resulting from the genotype and environmental influences. In the context of the lac operon, the genotype I⁺ P⁻ Oᶜ Z⁺ Y⁺ indicates specific mutations affecting the regulation and expression of the lac genes, which will influence the phenotype, particularly the ability to utilize lactose as a carbon source.