Part of total amount needed for Texas mission (5)
I believe the answer is:
alamo
'texas mission' is the definition.
(the Alamo Mission, fortress in Texas)
'part of total amount needed' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'ALAMO' is hidden in the letters of 'total amount needed'.
'for' acts as a link.
(Other definitions for alamo that I've seen before include "Texas fort famed for defence against Mexican army" , "Davy Crockett's last stand" , "US mission" , "don't forget it!" , "The --, Texan mission besieged in 1836" .)