Signalling Pathway: Which pathway is correct?

[TytoAlba95]

Homework Statement

In an organism, expression of gene ‘X’ is induced in the presence of a hormone. Genetic analysis showed that the hormonal signal is transduced through two proteins Let1 and Let2. The expression of gene ‘X’ was studied in lines over-expressing (OE) the active Let proteins, knock out (KO) of the Let proteins or combination of both.

Relevant Equations

Results of expression of gene ‘X’ in the presence of the hormone is summarized below:

Based on the above, which one of the following pathways best fits the observation made?

Correct ans is 2.
pg-315, sum-56

Attempt:

I think all the options are wrong, and the pathway should be

Option 2 is incorrect because if Let 1 is knocked out, the expression of X will stop as Let1 is needed to activate Let2.

Am I right?

 

[trurle]

Let2 "over-expression" mean the normal (WT) expression controls of Let2 are broken, and Let2 is expressed regardless of control signals. Therefore, last stage of pathway is "Let2 activates X", to which only answer (2) is matching.