= Solution
In a bacterial <transcription> complex, <RNA polymerase> binds a <promoter> and locally separates the <DNA> strands into a <transcription> bubble. The template enters the active site in the $3'$ to $5'$ direction, while the complementary <RNA> grows $5'$ to $3'$. The displaced non-template strand passes around the bubble, downstream <DNA> re-forms a duplex, and the nascent <RNA> exits through a separate channel. A short <RNA>–<DNA> hybrid is maintained in an elongating complex; the first few <nucleotides> of an initiating complex do not yet make a full elongation-length hybrid.
The core <enzyme> has subunit composition $\alpha_2\beta\beta'\omega$; association with a <sigma factor> forms a <promoter>-selective holoenzyme. Sigma recognizes <promoter> features and assists steps leading from a closed bound complex to the open complex. Different <sigma factors> redirect <transcription> towards different <promoter> classes. The familiar $-10$ and $-35$ elements are examples for a major bacterial sigma family, not a universal sequence rule for all <sigma factors>. <Promoter> escape changes these contacts, but complete sigma dissociation at one exact transcript length should not be assumed for every complex.
For the supplied non-template sequence, assuming its first base is the first transcribed position, the complementary template runs $3'$-TCAGTAAGC-$5'$. The <RNA> has the coding-strand order with <uracil> replacing <thymine>. Therefore the first five <nucleotides> are
$$
\boxed{5'\text{-AGUCA-}3'.}
$$
The top-left panel of the original schematic in part (d) shows the strand polarities and polymerase organisation; it is not a copied experimental illustration.
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