Manduca sexta vitellogenin is a phosphoglycolipoprotein (Mᵣ ∼ 500,000) that contains two copies of the apoproteins (apovitellogenin-I, Mᵣ 180,000 and apovitellogenin-II Mᵣ 45,000), 13 percent lipids, 3 percent carbohydrates and 0.6 percent phosphorus. The two apoproteins are immunologically distinct and apovitellogenin-II is not completely accessible to the aqueous environment in the intact molecule. The carbohydrate moiety located on apovitellogenin-I has a high mannose structure (Man₉ GlcNAc₂). Follicle membranes bind ¹²⁵I-labeled vitellogenin with high affinity and specificity (K(D) ≃ 1.3 x 10⁻⁸ M). Total binding sites were estimated at 4 x 10¹⁴ sites/g of follicle membrane protein. The binding was sensitive to pH and calcium. Competition studies showed that binding of vitellogenin was blocked by vitellin and deglycosylated vitellogenin but not by lipophorin, microvitellogenin or apovitellogenin-II. These results suggest that the uptake of vitellogenin involves binding to specific receptors on follicle membranes and the carbohydrate moiety and apovitellogenin-II are not involved in the interaction with the receptors.

Microvitellogenin is a female specific yolk protein from the tobacco hornworm moth Manduca sexta. A cDNA library was constructed from poly (A)⁺ RNA isolated from adult female fat body. cDNA clones of mRNA for microvitellogenin were isolated by screening the cDNA library with antiserum against microvitellogenin. The results of Northern blot analysis and hybrid selection indicated that the cDNA clone was specific for microvitellogenin. The complete nucleotide sequence of the 834 base pair cDNA insert has been determined by the dideoxy chain termination method. The deduced amino acid sequence was compared with the N-terminal sequence determined by Edman degradation, an amino terminal extension of 17 amino acids appeared to be a signal peptide. The cDNA sequence predicts that the mature microvitellogenin is a protein of 232 amino acids with a calculated molecular weight of 26,201. A comparison of the translated amino acid sequence with the sequences in National Biomedical Research Foundation protein library did not establish any sequence similarity with known proteins. The microvitellogenin gene begins to be expressed in the fat body on the first day of the wandering (prepupal) females as determined by using the cDNA insert as a probe to hybridize with the mRNA for microvitellogenin. The cDNA probe was also used to screen a genomic library of M. sexta, yielding three genomic clones for microvitellogenin. One of them was characterized and it contained the complete microvitellogenin gene. The gene sequence was determined. Comparison to the cDNA sequence showed that the microvitellogenin gene contains an intron near the 5'-end of the non-coding region. The 5'-flanking sequence of the gene has been compared to the same regions of yp genes of Drosophila and vitellogenin genes of locust, some similar sequences have been observed and discussed.