Works in ship and shipyards primarily in Northern Ireland and it's a chore (5,4,1,3)

'works in ship and shipyards primarily in northern ireland and' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'a chore' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'chore' could be 'job' ('job' can be a synonym of 'chore') and 'job' is found in the answer.
The remaining letters 'holdsdown' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

'it's' is the link.

Can you help me to learn more?