Nucleotide sequence of the intronless gene expressing a member of the globin VIIB subfamily fromChironomus thummi(Diptera)

Chironomus thummi fat body c e l l s s e c r e t e more than 10 d i f f e r e n t haemoglobins into the haemolymph during larval development ( l > . In contrast to the mosaic s t ruc ture of vertebrate and legume g lobin genes , the C. thummi genes encoding g l o b i n s III and IV contain no introns 1 2 / . Whether the g lobin III/IV subfamily l o s t i t s introns a f ter separation 350 m i l l i o n years ago (3) from other C. thummi qlobin subfamily l i n e a g e s , or whether lack, of introns i s a general feature of t h i s i n s e c t ' s g lobin genes i s not known. Screening a genomic l ibrary with the cDNA for globin VIIB-3 ( 4 ) , we i s o l a t e d a recombinant c lone with an 18 kb insert containing a c l u s t e r of g lobin VIIB subfamily genes . The sequence of one part of the c lone (below) inc ludes an i n t r o n l e s s g lobin gene (VIIB-4) which i s transcribed in the 4th instar (SI nuclease protec t ion a n a l y s i s not shown). Preliminary a n a l y s i s of d i f f e r e n t fragments of the 18 kb insert revealed other i n t r o n l e s s g lobin VIIB subfamily members, at least one of which i s transcribed and a l l of which have the s tructura l r e q u i s i t e s for t r a n s c r i p t i o n . Thus, absence of introns in expressed C. thummi globin genes i s not unique to the globin III /IV subfamily.