Let's analyze the function of the underlined nouns in each sentence:

1. **She is __a nurse__**
- Function: Predicate nominative (or subject complement). It renames or identifies the subject "she."

2. **__Your jeans__ are too tight.**
- Function: Subject. It is the noun phrase that serves as the subject of the sentence.

3. **John threw __the ball__.**
- Function: Direct object. It receives the action of the verb "threw" and answers the question "what did John throw?"

4. **__This jacket__ looks very nice and suits you well.**
- Function: Subject. It is the noun phrase that serves as the subject of the sentence, describing what looks nice and suits.

5. **__Tourism__ is __the main industry__ in the region.**
- Function:
- "Tourism" is a subject nominative (the subject of the sentence).
- "the main industry" is a predicate nominative, providing further identification of the subject "Tourism."

In summary:
1. Predicate nominative
2. Subject
3. Direct object
4. Subject
5. Subject (with "the main industry" as a predicate nominative).