There are 3 food allergens associated with turnip allergy. Bra r 1 is a 2S albumin protein. These are seed storage proteins most commonly found in nuts and seeds.
Bra r 2 is prohevein protein which is used in the plant for defence. Bra r 3 is a polcalcin protein. These are commonly called panallergens and are usually associated with airway allergens (pollens).
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Turnip.php
The allergy resources page for turnip covers the key allergens, which allergic syndromes are linked to this allergy and other foods which are commonly cross reactive with turnip.
There is also regularly updated links to useful websites specifically for turnip allergies and the latest research papers on the topic.
If you have multiple allergies and are interested in how they are linked or want to find out more about food allergies outside the usual top 14 then you can follow me on Facebook or Twitter, where I share a food allergy card every day of the week.